Less philosophy and more practicality this week. How best to prepare your mixes for mastering? It’s the age-old question, so here Donal’s Definitive Description!
I’ll start with the summary and go into detail below.
- WAV or AIF sound files
- Stereo interleaved
- The same sampling frequency (kHz) as it was recorded
- 24 bit resolution or higher
- No limiting, finalising or mastering plugins on the mix bus
- between 1 and 10dB headroom
WAV or AIF files
WAV or AIF files are the most common format that we receive these days.
Obviously if you can deliver the mixes on 1/2″ analogue tape, that’d be lovely, but otherwise sound files are fine. We can open most types of sound files, but there are sometimes compatibility issues, so using one of the two most common formats will ensure we can open them.
Stereo interleaved
We do sometimes receive separate mono files for left and right and often that’s not a problem, but if you send us stereo interleaved files then it will make things easier this end, and you’ll know that your stereo image will retain its integrity.
Sampling frequency
Create the sound files at whichever resolution the project’s been recorded at, eg if you’ve recorded at 48kHz, then give us files at 48kHz, or if you’ve recorded at 96kHz, send us files at 96kHz. Yes, it will end up at 44.1kHz on the CD, but the chances are the first thing we’ll do with the file is play it into a D-A converter and straight into some nice analogue gear, so the higher the resolution to start with the better it will sound the other end.
24 bit resolution or higher
A 24 bit digital signal has 48dB more dynamic range than a 16 bit signal (you get 6dB more headroom for every bit added). It’s always advisable to record at 24 bit or higher, but even if you’ve recorded the whole project at 16 bit, run the mix session at 24 bit because you’ll benefit from the increased headroom when mixing the individual 16 bit elements together.
Again, of course it’ll end up at 16 bit on the CD or digital download, but we’ll do all the mastering processing at 24 bit here and then gently fold that into a 16 bit signal using clever boffin-designed noise shaping dither, which can capture some of that higher resolution so that it’s audible when you play it at 16 bit.
Dither and noise shaping are amazing, practical applications of mathematical theory that you can actually hear. If you’re curious, check out http://en.wikipedia.org/wiki/Dithering and http://en.wikipedia.org/wiki/Noise_shaping.
Mix bus processors
Generally, you should always remove any limiters, finalisers, multi-band compressors or mastering plug-ins from the mix bus. Leaving these in severly limits what we can do with the mix, if you’ll pardon the pun. By definition, limiting distorts an audio signal by trimming off its peaks in order to then raise the level. Professional mastering studios have a number of limiting tools, both analogue and digital, that keep the distortion in areas that are less noticable and/or more pleasing to the human ear than most digital plugins.
If you love the sound of your limited/finalised mix, then send us that as reference, but also send us an uncompressed version to work with. Chances are we’ll get the same level, if not louder, and the mix will feel more dynamic and less distorted.
If you’re giving mixes to your client/band for reference and you want them to have something competitively loud to listen to, then by all means burn them a finalised CD at 16 bit, but run unlimited 24 bit mix files too, and mark that data CD “high resolution mix files for mastering”.
Headroom
I state between -1 and -10 dB of headroom, but the absolute number isn’t important so long as the highest peak in the song doesn’t hit 0dB on the digital meter. If it has then it’s probably been clipped so drop the level a touch and bounce again. Also, if you’re running at 24 bit then you’ve got 48dB more dynamic range than if you were at 16 bit, so even if your highest peak is at -10dB then you’ve still got 38dB more headroom than you would have had at 16 bit.
And of course, if you have any more questions about any of this, just leave a comment or drop me a line.
Tags: 16 bit, 24 bit, 44.1kHz, 48kHz, 96kHz, AIF, AIFF, analogue tape, CD, digital download, distortion, dither, dynamic range, finalizer, format, headroom, kHz, limiter, Mastering, mastering plugin, mix, mix bus, mix preparation, multi band compressor, noise shaping, sampling frequency, stereo image, stereo interleaved, WAV
