Stem Mixing

Mixing to stems has been common practice in sound for film and video for decades, but it is relatively new to the world of music production. Many people still don't comprehend that the mastering engineer cannot separate elements in a stereo mix and effect just that one element. For instance if he wants to brighten up the vocals in a stereo mix, everything else in the same frequency range will be brightened also. But if the mastering engineer has stems to work with he has a lot more flexibility and the result can be a much better finished product.

Stems are stereo (or mono) subgroupings of instruments or vocals. For example, the most common stem mixes have a stereo instrumental stem and a stereo vocal stem. When these two stems are set to unity gain (no volume boost or cut) and played through a common stereo output, you should have the complete stereo mix as the mixing engineer/producer intended it. But now if the mastering engineer needs to brighten up the vocals for instance, or thinks the guitars have too much midrange, then he can work with one stem without affecting the other. You might also have a case where the bass has been separated out to a mono stem of its own, so the mastering engineer can compress or eq it independently of everything else.

Stem mixing is really very simple. You don't do anything different until you're ready to bounce your mix. Mix as you normally would, get all of the instruments and vocals balanced, eq'd, panned and f/x'd until you're happy with the mix. Then mute all of the vocals and bounce your mix. You now have the instrumental stem. Then, unmute the vocals, mute everything else, and bounce again. You now have the vocal stem. If you load the two stems back in, set them for exactly the same start time, and play them both through the stereo output, voila! You are hearing your stereo mix just as you wanted. If you have done things correctly, listen to the instrumental stem and you will hear that all of your automated fader moves, f/x etc. have been printed with that stem. You should hear no vocals, vocal reverb, echo or anything else related to the vocals. Likewise if you listen to the vocal stem there should be no hint of instruments or instrument f/x.

So you see it would be the exact same procedure if you wanted to separate out bass, background vocals, drums, whatever. You just mute everything else in the mix except those elements and print. But the mastering engineer would prefer you keep it as simple as possible, the ideal being an instrumental stem and a vocal stem as in the example above. Don't distract the mastering engineer by delivering too many stems in one song so that he is suddenly having to listen like a mix engineer and not a mastering engineer (two VERY different ways of listening, btw).

If you are mixing through an analog console with analog f/x, you need to be very conscious of processor noise. When you are printing your vocal stem, you should mute all f/x processors that are dedicated to instruments only, or if you have dedicated returns for instrument f/x then those should be muted. Otherwise you will be printing the noise from your instrument f/x processors onto the vocal stem, and then you will get the noise again when you print the instrumental stem. Although it may seem like a minor detail, you should do the same when you print the instrumental stem regarding the vocal f/x returns. Even on loud tracks, every little bit of noise you can eliminate will make a difference in the final product.

In the hip-hop world, delivering stems for a single can make your life much easier. All you need to deliver is the instrumental and vocal stem for each song. Now the mastering engineer can add the two together for the club version, mute the bad words on the vocal stem for the radio version, instrumental stem only for instrumental version, vocal stem only for acapella version. Too easy. (Or save a little money and do a clean vocal stem yourself if there are a lot of words that need to be muted).

Make sure you talk to your mastering engineer before you deliver stems. Not all mastering rooms are as technically hip and savvy as DES Mastering (shameless plug), so you shouldn't assume that they can work with stems.

Master, Master, Who's Got the Master?

There's a lot of confusion concerning what a 'master' is. One problem is, too many things are called masters. If you have a 'master', hopefully it will be labeled with one of the following terms. Or if you are in production, and you want to do yourself, your client and anyone else down the production chain a huge favor, learn and use these terms. For these purposes we'll talk about stereo only. Surround opens a whole different can of worms. Here we go!

MULTITRACK MASTER, TRACK MASTER

This is the master containing the unmixed tracks from the recording session. They range from 2 to 32 tracks in analog tape formats, up to 48 tracks in digital tape formats, and 128 tracks and beyond on computer-based systems. On modern track masters, each instrument and voice is still on a separate track. On track masters from around 1967/68 and before, you would have two, three or four tracks of combined or compiled (comp'd) recordings. Say if you had the final 4-track master from Sgt. Pepper, on those four tracks you might have all of the Beatle's rhythm section on one track, the London philharmonic on a second, a percussion section on a third, and all of the Beatles vocals on the fourth. Regardless of the number of tracks, these masters have to be mixed to stereo (or mono) before you proceed to mastering and manufacturing. They can be analog or digital reel-to-reel tapes of varying sizes, audio cassettes, VHS or Hi-8 video cartridges, and these days thumb, USB or Firewire drives, data CD-Rs or DVDs.

STEM MASTER

Mixing audio in stems has been commonplace in the film and video industry for decades, and is becoming increasingly popular in music production. Stems are stereo or mono subgroup mixes that are then combined for the complete stereo mix. In music for instance you could mix a stereo vocal stem, a stereo instrumental stem minus bass, and a mono bass stem. This would allow the producer to easily create a vocal up version for radio, edit the vocal for a clean version, pump up the bass for a club version etc. In mastering, stems allow the engineer to process and control the individual stems rather than having to process the entire mix. Stem masters could be any of the same formats as the track masters above.

MIX MASTER, MIXES, MIX FILES, BOUNCES, BOUNCE FILES, SOURCE MASTER (in mastering terminology)

These contain the stereo mixes that have not been edited or mastered. These can be various sizes of analog or digital reel-to-reel, analog cassette tape, VHS, Beta or Hi-8 video tape, DAT tapes, audio CD-Rs, or folders containing audio files on data CD-R, DVD or any form of hard drive.

For people who record and mix 'in the box': Do not be a lazy engineer. Your individual tracks in your session folder should have proper file names, "Kick", "Snare" etc., not "Track 1", "Track 2"... Your mixes should be in one folder labeled as "Mix Masters" etc.

EDIT MASTER, BANDED MASTER, SEQUENCE MASTER, SEQ MASTER

In the analog days of vinyl, this referred to an analog mix master tape that has been sequenced and topped & tailed (noise before and after each song edited out), timed leader tape has been inserted between tracks for proper spacing, and leader tape has been added to the head and tail of the reel. It also implies that any inner-song editing has been done. In the analog days we would say these tapes have been 'prepped', meaning the tape has been prepared for the cutting room. Unless otherwise noted, this master has not had any further processing such as eq, compression or limiting, which was done at the lathe as the lacquer was cut. In today's world, mastering engineers prefer that you do not top or tail your mixes, leave a second or two of noise before and after the audio.

In the digital age, a BANDED MASTER has a new meaning. Many artists want to have some or all songs on their album crossfade between each other, have no space between tracks etc. But of course this can cause problems in the age of downloads since the ending of a song that crossfades into another song will just suddenly chop off if you download the first song only. Or if you download the second song, you hear the end of the first song fading out as the song you wanted starts. So many artists have their mastering engineer create a 'banded master' which has a basic 2 seconds or so of silence between songs. They will use this as the source for online content so the songs have clean in's and out's. This also allows them to suggest purchasing the CD if the listener wants to hear the album the way it was really intended. Unlike the analog version, this type of banded master would be implied to have all mastering processing applied. These banded masters can be on any of the media described in the next category.

PRODUCTION MASTER, PRE-MASTER, EQ MASTER, EQ AND LIMITED MASTER, PMCD, REFERENCE MASTER, GOLD DISC MASTER, DDP, DDPi

A master that has any of these labels would be assumed to have all mixing, editing, sequencing and masteering applied and is ready for manufacturing as is. Some of these need further explanation:

PRODUCTION MASTER, PRE-MASTER, EQ MASTER, EQ AND LIMITED MASTER - The standard media that manufacturers can or could accept that would have one of these labels would be analog or digital reel-to-reel tape of varying sizes, VHS, Beta, Hi-8, and 3/4" U-Matic video tape, audio cassette tape, DAT tape, red-book standard audio CD-R, and now some manufacturers will accept production master audio files on data CD-R, DVD, any type of hard drive or as uploads to a server. 'EQ Master' and 'EQ and Limited Master' are old-school terms for labeling production master reel-to-reels that were prepped for the cutting room. If your mastering guy uses one of these terms you can be pretty sure he's been around the block.

PMCD, REFERENCE MASTER, GOLD DISC MASTER - These would only apply to a CD-R. The definition of PMCD has changed. Originally, this meant 'Pre-Master CD'. This was a revolution in CD manufacturing that was developed by Sonic Solutions and allowed CD plants to cut glass (explained below) directly from a CD-R, eliminating a very expensive step that will be explained later. The Pre-Master CD was a CD-R that could only be created on Sonic Solutions mastering systems and contained a data burst that fed the TOC (table of contents) timecode information into the glass mastering program independent of the audio. Probably no, or at least very few, CD plants can use Pre-Master CDs any longer, as the CD burners that Sonic needed to create them have been obsolete for about 15 years. And now CD plants can cut glass from ordinary red-book standard audio CD-Rs. These audio CD-R production masters were originally referred to as a Reference Master or a Gold Disc Master (even though the disc may be silver or green). Some still use those terms, but increasingly they are referred to as a PMCD, now meaning 'Production Master CD'. A CD-R with one of these labels would normally be for CD replication, but often production masters for vinyl records or in the days of cassettes would have the same label. If you have a master that is labeled 'PMCD', there is really no way of telling which type it is if you don't have a Sonic Solutions system with the proper CD drive. But never fear, a Pre-Master CD will play on a normal player, and can be used by a CD plant, just like a current Production Master CD.

DDP - The DDP (Disc Description Protocol) is acknowledged as the superior production master for any optical disc medium - CD, DVD or Blu Ray. The DDP is an absolutely error-free master, which creates a superior sounding CD in the case of audio, and also creates CDs that are more reliably played by cheap CD players, boom boxes, car players etc. The DDP breaks the audio, subcodes, TOC and metadata down into separate elements, and is delivered on an 8mm video cassette created by a machine called an Exabyte. The downside is that it is still a mechanical tape cartridge, which can fail, and it requires a specific, costly machine at both the mastering room and the CD plant. So enter the future, and for some, the present:

DDPi - DDPi is a 'Disc Description Protocol image'. and is the new standard in production masters for any optical disc, including audio CDs. It contains all of the elements on a DDP Exabyte tape, but it is written directly to a hard drive in the mastering room and can then be delivered to the CD plant on a data CD-R or DVD or it can be uploaded directly to a CD plant's server. The only downside, if you want to call it that, is that you have to use a cutting edge mastering room that understands and can create a DDPi file set, like DES Mastering (www.desmastering.com) for instance, and you have to use a CD manufacturer that can utilize the technology, which coincidentally DES can steer you to.

The reason Sonic Solutions (now SonicStudio) workstations, as used by DES, have been the mastering industry's standard for 20+ years is not only because of their superior sound quality but because Sonic writes the absolutely lowest error PMCD compared to any other system. However, you would probably be shocked to see how many errors even these comparatively low-error masters have, and these translate directly to your manufactured CDs. The thing is, a CD player has a certain amount of DSP (digital signal processing) allocated for error correction. The amount of DSP being performed will directly affect the sound quality of the playback. So the fewer errors on the CD, the better the sound. That is why real mastering rooms use very specific software and burners. If the person doing your mastering is using standard off-the-shelf CD burners and software, you are losing sound quality. So to emphasize the advantage of DDPi, it is an error-locked system, meaning it is either 100% accurate or 100% fail. If it works, it is absolutely error-free, yielding the best sounding CDs possible. But rest assured that even if you are already using a plant that can only accept Production Master CDs, DES Mastering can provide you with the best quality master possible. OK, enough commercials; onward, through the fog!

Now things get a little tricky, because we have a difference in terminology between Europe and the U.S. In the U.S., what we do at DES (eq, compression, limiting, song sequencing, spacing etc.) is called 'mastering'. In Europe, this is called 'pre-mastering', and 'mastering' means that you are creating a part that will be used in manufacturing; cutting lacquer for vinyl, cutting glass for CD replication (we'll get to that) etc., and this is also called mastering in the U.S., which causes some confusion.

PCM-1610, PCM-1630

Before Sonic created the Pre-Master CD, anything going to CD replication had to be on either a Sony PCM-1610 or PCM-1630 formatted tape. Simply put, these were like gigantic DAT machines with a couple of extra analog data tracks where timecode and pq subcode info was put. The converter itself was probably 30"wx24"hx30"d and weighed 100 lbs. or so. Rather than a tiny DAT tape the digital audio was recorded onto a professional 3/4" U-Matic video tape, which required an enormous video deck. If I remember correctly, the cost of the converter with the video deck was around $25-$30,000.00. Of course smaller mastering rooms couldn't afford this, so some CD plants would allow Production Master DATs that they would then format to their 1630, for an extra fee of course. If the only master you have is one of these U-Matic tapes, there are still mastering rooms that have a 1630 system and can get your material onto a more usable format, but you would be advised to do this asap. If you need this contact us at george@desmastering.com and we will refer you to the proper people.

GLASS MASTER

Boy, does this cause a lot of confusion. With only the rarest of exceptions, glass mastering is only done at your CD plant. A few of the super high-end (and priced) mastering facilities may cut glass, but they are few. Even a lot of people who consider themselves mastering engineers get it wrong and will call the PMCD (or Reference Master or Gold Disc Master, as you now know) they create a Glass Master. Getting back to the terminology thing; the CD plant uses the European terminology - the processing and assembly done by DES for instance to create a PMCD or DDPi would be 'pre-mastering', cutting the glass at the plant from this would be the 'mastering'. This causes confusion when a plant says that mastering is included in their pricing. What they are talking about is cutting the glass master. Their price does not included pre-mastering.

The glass master is a large glass disc approx. 240mm in diameter that is painted with photo-resist. Then the digital audio from the PMCD, DDP, DDPi or PCM-1610/1630 is photo etched onto this using an LBR (Laser Beam Recorder). Stampers are then created from this and the photo-resist is peeled off the glass which is then highly polished to be used again. So the CD plant will only have a limited number of glass discs that are used over and over. This is the CD equivalent of cutting lacquer for vinyl records.

A note about production masters for download-only releases:

At the very least, this should be a PMCD. Online stores such as iTunes and CD Baby will not allow you to upload your own mp3s or AACs. They want the full resolution, CD-quality audio files. That way, not only can they create the best quality compressed files with their own CODECs, but as technology improves, like when iTunes went to iTunes+, they can create a new set of compressed files from your full-resolution upload. Hopefully, as connection speeds increase and storage gets cheaper, we will be downloading full CD-quality music, or even better.

As we've said before, you should NEVER accept an mp3, AAC or any other data compressed file as a mix master or production master. See our entry "Audio Production in the Age of mp3 and AAC" http://desmastering.blogspot.com/2009/09/audio-production-in-age-of-mp3-and-aac.html.

I intended to include a list here covering a question that we mastering guys hear all of time time; "I've found this (fill in the blank) type of tape/disc from an old session. What could this be?", but this has already gone longer than I expected. I'll do that next entry.

What is Acceptable as a Master?

As the home recording 'revolution' continues, we are seeing more and more people charging for professional audio services but who apparently have no idea about standards that have to be met in order to assure the best audio quality, and what to give their clients so they can proceed to post-production, mastering and manufacturing. There is a disturbing trend, especially in the hip-hop community, of studios, producers and so-called mastering engineers delivering mp3s as masters.

PLEASE MAKE NOTE - MP3 IS BARELY ACCEPTABLE AS A CONSUMER FORMAT. IT IS NOT ACCEPTABLE AS A MIX MASTER, PRODUCTION MASTER OR FOR ANY OTHER PROFESSIONAL APPLICATION!

The only thing in professional production that mp3 is used for is as a quick reference that can be uploaded for a client to approve a mix, an edit or a revision etc. Also, most stadium and arena music comes from mp3, but that is hardly a critical listening environment.

If you mix to a digital recording system, when you leave the studio you should have your mixes in as high resolution digital format as possible. Refer to our blog entry of Sept. 15, 2009 "Audio File Formats, Sample Rates and Bit Depth" for a detailed explanation. But in brief, your mixes should be .wav, .aif or .sd2 audio files of at least 24 bit resolution and at the same sample rate your session was tracked at. In other words no sample rate conversion should have been performed. Also, be sure you get your 1st generation, unprocessed mixes. That means no normalizing, fades, edits or any other process has been applied. You might also have a folder of Edit Masters which have fades & edits (normalizing shouldn't be done in any case), but for mastering you want the totally unaffected mix masters.

It's a good idea for you to take a hard drive to the studio and have them put your high res audio files there, or the studio may have priced a drive in your package, but you should also have them create one or more data CD-Rs or DVDs containing your mixes. I've seen it before; artists who think they've done the right thing by storing all of their mixes and sessions on a hard drive, only to have the drive fail. Having them on a hard medium like CD-R or DVD is the safest backup. Of course you also want the studio to provide you with an audio CD-R reference disc so you can easily proof your mixes, but for your archive and for mastering, post production etc. they should be high resolution .aif or .wav or .sd2 audio files.

Remember, It's Not Art, It's Noise

In my opinion this should be required reading for all engineers and rock musicians. We are making rock music too perfect with one technology, and destroying it sonically with another.

http://www.npr.org/blogs/monitormix/2009/11/the_death_of_mistakes_means_th.html

Mixing in Preparation for Mastering - Part 2 - Levels

One of the biggest mistakes that mixing engineers make who have not dealt with a mastering room before is endeavoring to make their mixes as loud as an off-the-shelf CD. This is totally counterproductive. The final loudness of the CD is one of the issues addressed by the mastering engineer. Unfortunately many think that making the CD loud is all that mastering is. It is one of the elements of mastering, but certainly not the most important. Your source mixes should be at a relatively low level. Ideally, on a 24 bit mix the hottest peaks should hit somewhere around -6dBfs (dB full scale, meaning 6dB below zero full scale on your digital output meter). This means the average or V.U. level should be around -18 to -20dBfs.

You want to do this for two reasons: First, some of the top golden ears in our industry have determined that almost all workstations and a-to-d converters work and sound best at this 0v.u.=-18dBfs range. Whether you are mixing through an analog mixer or summing amp or in-the-box you will hear a very noticeable improvement in the clarity and space of your overall mix, especially in the vocal range. The vocals seem a lot less stressed and crowded, everything seems to breath better. Probably not coincidentally, this is the 'standard' that Sony and Phillips set for average level when they introduced the PCM digital format that we use today. The problem is it was never enforced as a true standard, so mastering and mix engineers were allowed to make CD masters as hot as they pleased, which has ruined the quality of many potentially landmark recordings since around 1995 which is when the first ridiculously loud CD's began being produced. We'll address the 'loudness wars' in a future blog entry.

The second reason you should not crowd 0dBfs on your mixes is that digital mastering processors need some headroom to work at their best. If a mix is slamming all the way to digital 0, the mastering engineer has to lower its level before he can do any digital processing, which means he's performed a dsp step before any processing has been done, and the signal quality has been slightly degraded.

The upshot of this is you should not apply any eq, compression or limiting across the stereo buss as you mix if it is for the purpose of making the mix louder.

If you mix at lower levels and without stereo buss processing as described above, the mastering engineer has his/her complete palette of tools to choose from. If the mix has not been compressed or eq'd he can choose digital, solid state analog, tube analog or any combination of processors to get the best sound possible.

Caveat: If you are using a buss compressor to get a particular compressed sound, as is often heard in heavy metal, or a rhythmic pumping you might hear in some electro-pop or dance music, and you can't get the flavor of mix you want without it, then by all means use it. But again it should be to add a particular color to the mix, not to make it loud. If you are unsure, print one mix without buss processing and another with so the mastering engineer can choose which works best for the end result.

Most problems with dynamics will usually come from drums and percussion. If you have problems with your drum tracks being too dynamic, don't compress the entire mix, assign the drums to their own subgroup and add a compressor/limiter across that group alone. This would apply to any group of instruments/vocals that you are having trouble getting to sit properly in the mix.

TWO METHODS FOR ACHIEVING -18DBFS AVERAGE LEVELS

If you are mixing through an analog console or summing amp, route a 1khz tone to the stereo output and adjust its gain so your master output V.U. meter reads 0. Then adjust the input sensitivity of the A-to-D converter that you are mixing to so its digital peak meter reads -18dBfs. Now if you mix so your output V.U. hovers around 0, you'll be hitting the digital recorder at that ideal -18dBfs average level. Some engineers prefer lower average levels of -20dBfs and even as low as -24dBfs. Experiment and listen to mixes at these different levels to learn where your A-to-D converter sounds best.

Here's a million dollar tip if you are recording and mixing in-the-box: The trick in all-digital recording and mixing is to learn to record your individual tracks at a lower level, so that during the mix you can have your channel faders close to unity gain (no boost or cut) and your master fader at unity gain, and the resultant mix be hitting that ideal 0v.u.=-18dBfs to -20dBfs range, which should put your peaks around -6dBfs. Here's the deal; the more you are boosting or cutting the level of a channel during a mix, the more dsp you are performing and the more digital artifacts you are creating. Many engineers have learned the technique of setting their monitor faders at unity gain, and then recording the individual tracks so they are getting close to an ideal mix without having to move any monitor faders up or down, and again where the average level of the monitor mix is hovering around -18dBfs. Then during the mixdown they most often have to adjust the channel faders no more than a dB or so to fine tune the mix. This takes a lot of practice to get right, as you will eventually be recording your tracks at a lower level than you are used to, but the result is a mix that has a depth and clarity to it that you've probably not achieved before.

MAJOR CAVEAT: The above only applies if you are tracking at 24 bit resolution. By employing this technique some of your tracks may be recorded at a very low level. The digital noise floor of a 24 bit recording is so far down that this isn't an issue, but a 16 bit recording is a different matter, and if you record low level tracks at 16 bit you will probably have a hashy mess when you mix. If you are tracking at 16 bits you should endeavor to record each track within 2 or 3dB of 0 full scale.

You should not worry about the perceived volumes of your songs being different. Again one of the jobs of the mastering engineer is to match the perceived levels as well as eq so there is a consistency to the tracks in both volume and tonal balance.

Many engineers have already learned that mixing at the proper levels for mastering can potentially cause a problem: If they give their clients a reference CD of the mixes that is half the volume of an off-the-shelf CD or lower, then the client will likely freak out. So now it is common practice for many engineers to do proper 24 bit high resolution, low level mixes to be delivered for mastering, and then add a limiter across the stereo buss, crank up the level and run the mixes again for making the client's reference disc.

Mixing in Preparation for Mastering - Part 1: Audio File Formats, Sample Rates & Bit Depths

In order for your mastered tracks to have that sparkle and clarity that you envision, it is important to follow some mixing guidelines. For these discussions we'll assume the project is for CD-Audio, but all the basics apply no matter what the final delivery medium.

First we'll address digital audio file formats, sample rates and bit depths.

1.) DO NOT SAMPLE RATE CONVERT. If you are mixing 'in the box' or through an external digital mixer, the mix files should be at the same sampling rate as the session. That means NO SAMPLE RATE CONVERSION. Hopefully you tracked at 48k or ideally 88.2k or 96k, but many engineers make what seems a logical assumption that since CD-Audio has to be 44.1k, then they should convert their mixes to 44.1k even though the session was tracked at a higher sample rate. There are three reasons not to do this. First, for ultimate sound quality the project should be mastered at the higher sample rate at 24 bits and then downconverted to 44.1/16 as the final step before the Production Master CD or DDPi is cut. Second, it is likely that a real mastering room has a much better sample rate converter than those found in even large studios. And third, there is a growing trend of artists and sites offering hi-resolution downloads, so it is advisable to have the mastering room create a separate data master containing the mastered 24 bit files at the higher sample rate.

2). MIX AT 24 BIT RESOLUTION. Even though your session may have been tracked at 16 bit, it is important to mix at 24 bit resolution. The reason is that if you do anything more than play one sound file at unity gain out of one buss, even something as simple as changing the gain by 1/10th of a dB, your system has to expand to a 24 bit word length internally. So if you output your mix as a 16 bit file, you will create truncation distortion and lose fidelity. Since hard drives are so inexpensive these days, you really should be tracking as well as mixing at 24 bit resolution.

In the mastering world we are seeing a disturbing trend of people wanting to deliver mp3's as sources. mp3 is barely acceptable as a consumer audio format, and is certainly not suitable for mastering.

CAVEAT: Know Your System! If your DAW or digital mixer operates at 32 bit or 32 bit floating, you need to apply 24 bit dither if you are outputting 24 bit mix files. Or you should output them as 32 bit files and inform the mastering room of this.

Relating to points 1 & 2, There is no 'getting back' quality. If you have created 16 bit mixes, loading them into a program that will output them as 24 bit files will do nothing for you. All it will do is add 0's to the lower eight bits. The sound quality will be the same but the file will just take up more disk space. Likewise upsampling a 44.1k file to a higher sample rate will often decrease quality except in the best of sample rate converters, and then the quality will likely be the same, it will again just take up more disk space. If all you have are mp3's of your mixes, converting them to .aif or .wav will not improve their quality. In fact, you will lose quality with such 'transcoding'. If all you have are mp3's any qualified mastering engineer will know how to handle them to result in the best quality possible. The same is true if all you have is an audio CD-R for a master - it's not doom, many great records have been made from 44.1/16 masters.

3) AUDIO FILE FORMATS. All mastering rooms should accept any of the standard file formats - .aif, .wav, .bwf or .sd2. Normally interleaved stereo files are preferred at the mastering room, but split L/R is fine and there is no difference in fidelity. Also, keep your file names under 15 characters. It's not necessary to name the file with the full song title. Just the first two or three words of the title is fine. See the documentation topic below.

4.) DELIVERY MEDIUM. Most mastering rooms should offer you the option of uploading your mixes. You should put all of your mix files into one folder and then zip that folder prior to uploading. Zipping a folder will perform and internal checksum which ensures that nothing was corrupted during the upload/download. If you want to deliver your mixes on disc, make sure you are creating either a data CD-R or DVD, not an audio CD-R. If you have tracked and mixed at 48k or above at 24 bits, and then you put your files onto an audio CD-R, you have lost fidelity. The reason is that an audio CD-R, like CD-Audio, can only be 44.1k/16 bit, so even though you may not realize it your CD burning software has converted your files to 44.1k and then dropped the lower 8 bits, and you have lost fidelity through both an inferior sample rate conversion and the file has been truncated. On a data CD-R or DVD, the audio files can be of any sample rate and any bit depth. Plus the method in which a data disc is written is much more accurate than an audio CD-R, so there are no errors on the data disc. Your 24 bit higher-sample rate files are much larger than CD-Audio files, so an album's worth will fit on one DVD-R, but will require 2 or more CD-R's, which is fine.

Any mastering room should also accept your sources on a Firewire or USB drive.

5.) MULTIPLE SAMPLE RATES. Do not mix sample rates unless clearly noted. Mixed sample rates often occur when multiple studios and/or engineers have been involved in a project. One engineer may have tracked and mixed at 48k, another at 88.2k etc. If you have a situation where your mixes are at different sample rates, put them into separate folders indicating the sample rate of the files they contain. Bit depth does not matter, if some of your mixes are 16 bit and some 24 bit but all are at the same sample rate this will not cause a problem at the mastering stage.

6.) EDITING AND OTHER PROCESSING. It is important that you deliver the first generation mix files for mastering when possible. They should not be loaded into any program to convert .aif to .wav, or split L/R to interleaved or any other seemingly transparent process. They ESPECIALLY should not be loaded into any workstation for normalizing, fades, edits etc. Your mastering engineer can easily perform fades and edits, and normalizing should not be done in any case. In most cases eq, compression or limiting should not be applied across the stereo buss while mixing. We'll address that in the next post.

CAVEAT: If your project will require a lot of editing, sometimes budget will not allow editing in the mastering room. If you do your editing in the studio, just be sure that everything stays 24 bit, the sample rate stays the same and that no level changes are done if at all possible. If your editing requires a section of a song to be raised or lowered in volume, then 24 bit dither should be applied when the finished edit is output.

7.) DOCUMENT, DOCUMENT, DOCUMENT. Too much information is a good thing. Your sources should be delivered with documentation indicating the sample rate and bit depth of the files as well as the title of the file and the corresponding full title of the song. It is also helpful if your mix engineer can provide details of whether the mix was done in the digital domain or through an analog mixer, if analog tape was used at any stage and whether stereo buss processing was applied and if so what kind and how much was applied and if any dither has been applied at any stage.

8.) ONLINE DELIVERY. If you are going to make your finished project available through download only, do not assume that you can lower the quality of any steps in your production. Please read our first blog entry Audio Production in the Age of mp3 and AAC for details.

Don't Forget the Future - Archive Your Music

3/24/11 - Some very important news you need to read concerning archiving. After you read this post, please go to Alarming News.

When an artist/producer finishes a project, they are often so beaten down by it that they don't think of ordering at least a production master for their own archive. (Archiving means to store important information for a long period of time.) And by the time they realize this it may be too late to obtain one. Many CD plants will not return the Production Master CD (PMCD) or DDPi that you send them. That way you are locked into using them for additional runs. Glass masters are not archived at CD plants as many tend to think. A CD plant will only have a certain number of glass discs that are then re-used over and over again. If you order a new run of CDs they will cut glass again from your master that they have on file. Or in some cases the plant creates an image file of your PMCD, or copies your DDPi to their drives, and then destroys the actual disc. And what many have learned the hard way, most of the ads you see for CD manufacturing are not CD plants, but brokers acting as a go-between that normally use several different plants. So as those people go out of business, there is often no record of what CD plant was actually used for a given project, so the master is lost.

But producers, artists and labels should consider not only having an additional PMCD or DDPi of their own, but a data backup of the mastered project in high resolution as well. Here is how it works in the mastering process (if you are dealing with a real mastering room):

Ideally your original source mixes were at 24 bit resolution, and mixed at the same sample rate at which the session was tracked. And hopefully it was tracked at 88.2 or 96khz. Regardless, the mix engineer should not have sample-rate converted the mixes. We know that CD-Audio can only be 44.1khz, 16 bit resolution. But the mastering should be done at the higher sample rate of the sources and at 24 bit resolution, then downconverting to 44.1/16 should be the final step before the PMCD or DDPi is cut. Even in the worst case where the source mixes were delivered at 44.1/16, the mastering will still be done at the 24 bit level. So you can still get mastered files at 44.1k/24 bit, which will have a sound superior to the CD.

So why would you want these high resolution files? We can look at two possible scenarios:

First, if we follow the current trend where the majority of audio will be delivered online, and if things stay at the relatively lo-fi of our current mp3 and AAC formats, then you will have the best sounding masters possible to create new bit-reduced files as you need or as technology changes. As I explained in my first post, your master has to be of the utmost quality if the bit-reduced versions are going to sound decent. So if you have mastered files at a higher resolution than even CD-Audio, then any down-converted files you create from them are all the better.

Second, and more importantly, we are now seeing what industry insiders have predicted (hoped for) for a couple of years - that as internet speeds increase, and as storage gets smaller and cheaper, we will see high-resolution download options for consumers interested in better sound quality. You now see many bands offering at least CD resolution WAV files and even better on their personal sites as a more expensive option to the mp3 download. Radiohead's "King of Limbs" was offered as 44.1/16 WAVs for instance. And we are beginning to see sights like hdtracks.com that offer current and classic albums in as high as 176.2k/24 bit! So as this trend hopefully continues you will eventually (or even now) be able to offer high-resolution downloads of your music.

1/18/12 - Click Here for important update on tracking and mixing in HD.

Less likely, if a new high-resolution consumer audio format is released that is actually accepted by the general public, then you have high-resolution mastered files that you can release on the new format. Unfortunately, DVD-Audio and SACD were miserable failures. And the majors aren't likely to get behind any new hard delivery mediums anytime soon, if ever. 

A qualified mastering room will be able to offer a DVD containing your high-resolution mastered tracks as well as a Production Master DDPi file set for CD manufacturing, and your unmastered source mixes. At DES Mastering it is our standard practice to also include text files of the pq and delivery logs, metadata verification as well as mastering details. Ideally you would get both a Production Master CD and a data DVD as described for your archive. As this will probably run a few hundred dollars, you should be able to arrange with your mastering room to have all of this created at a later date. Mastering rooms can usually create archival masters within a two or three month period after the project is finished.

IF YOU HAVE DAT MASTERS, YOU NEED TO GET THEM TRANSFERRED NOW!!!

If you have important music on DATs you need to get them transferred to standard audio files as soon as you can. There are two reasons for this; number one is that the DAT is a mechanical format that is subject to failure. Even in mastering rooms with well maintained machines a snag can happen and a tape can be ruined. Also, depending on how the tape was stored, the data can become unreadable.

One of the biggest reasons however is that DAT machines are no longer made, and are no longer commonly seen in most studios. And fewer and fewer technicians can repair them or have access to parts. So before they all go away, get your DATs transferred!