Ok, so you just finished your new project and it’s time to mix. What the hell format do I mix to?

In the "Good Ole Days" it was easy. You printed your mixes on 1/4" analog tape. You had a few choices to make, but not many. The tape speed for the mixes could be 15 ips or 30 ips. 15 ips gave you better low end, while 30 ips gave you a lower noise floor and an extended high frequency response. You then had the choice between no noise reduction, or Dolby A noise reduction. (Dolby SR didn’t show up on the scene until after digital machines became available. There were a few people who used DBX noise reduction, but I think they all killed themselves.) Then along came digital.

Now there are about a gazillion (should gazillion be capitalized?) formats to choose from. There are still those who mix to analog, but now they have the additional choices of 1/2" and 1" tape. There is even some nut trying to build a 2" two track analog machine for mixing.

Remember that a 10 1/2" reel of tape only records 15 minutes at 30 ips (unless you use thin tape, which increases the print-through.) To get 30 minutes on one roll of tape it has to be on a 14" reel.

Digital Pro Formats

In the Pro arena, Sony built the original 3/4 inch video based PCM-1610 digital audio recorder (and later the PCM-1630) that became the standard for CD mastering. The sample rate was 44.1kHz, 16 bits. JVC also had a 3/4-inch video system for CD mastering. Sony later introduced the PCM-3402 1/4-inch reel to reel machine that recorded 16 bits at 48kHz and 44.1kHz. Mitsubishi made the X-80 reel to reel machine that recorded 48kHz only at 16 bits. (George Duke and I had the first two machines. They originally recorded at 50.4kHz) Mitsubishi later introduced the X-86 and the X-86-HS. The HS version would record at 44.1kHz, 48kHz, 88.2kHz and 96kHz, all at 16 bits. All of these machines have been discontinued, but there are enough of them still around that they still get used for mixes and CD mastering.

DAT’s A Choice You Have To Make

To start with, we will consider DAT machines. There are a plethora of choices when it comes to DAT machines. All DAT machines are not created equal. If you are mixing on an analog console, you have to convert the signal to digital somewhere along the line. Some DAT machines have better built-in converters than other DAT machines. Some engineers use external converters that connect to the digital inputs of the DAT machines. A lot of choices to make just to get your mixes on a piece of DAT tape. DAT tape only records 16 bits of information. If you see a DAT machine that boasts 18 bit or 20 bit converters, you may end up with a better quality converter, but only 16 bits of the 20 bits gets stored on tape.

Some Sony DAT machines have built-in Super Bit Mapping software that increases the resolution of the 16 bits on tape. With a 20 bit converter, the Super Bit Mapping makes the 16 bit signal sound like a raw 18 bit signal (about halfway between the quality of 16 bit and 20 bit.) The Super Bit Mapping option only works on the analog signal into the DAT machine, and is bypassed when fed with a digital signal, so you can’t use the internal Super Bit Mapping software to crunch a 24 bit signal from and external converter. Sony does sell a stand-alone Super Bit Mapping box that will work with external converters, but it costs more than the DAT machine.

This method of getting more resolution than you have bits is called noise shaping. When I am asked how noise shaping works, my answer is, "Just fine!" That is as much of an answer as I have room for here. Apogee also has a noise shaping system called UV-22. UV-22 is built into most of Apogee’s converters. You can use a 24-bit apogee converter, switch on UV-22 processing, and get a very good 16-bit signal to record on DAT.

One step down from noise shaping is dithering. Dithering lowers the noise floor and allows you to hear very low level signals near the bottom of the 16 bit boundary. Dithering only works on the lowest one or two bits of the signal. There are different algorithms for dithering; so if you have a choice, listen and decide which version you like best.

Consumer DAT machines will only record at 48kHz when the analog input is used. Copy protection flags are set so that you can’t make digital copies of tapes that were recorded in another consumer machine. Semi-pro DAT machines ignore copy flags when fed a digital source and let you record at 44.1kHz or 48kHz when fed with an analog source.

With the introduction of 24bit technology and 96kHz sample rates, most DAT machines are left in the dust. Pioneer makes a DAT machine that will record at 96kHz, but only at 16-bit resolution. Tascam makes a DAT machine that will record 24bits, but only at 48kHz or 44.1kHz. (I’ve got it! You could record on both machines at the same time, and then later merge the two files in a computer. You would have a 96kHz file and every other sample would be 24 bits!)

And finally, HDCD, a process invented by Pacific Microsonics, is an encode/ decode system that will store more than 16 bits worth of information in the 16 bit data. If you have a HDCD equipped CD player, you will hear the high-resolution signal during playback. If you do not have the decoder, then you will hear the 16-bit signal with some additional noise shaping benefits.

In the low-resolution category (16 bit 48kHz or 44.1kHz) there are other places to store your mixes. The most common format is audio CD. The resolution is stuck at 44.1kHz 16 bits, but if the ultimate destination is CD then you are well on your way. There are numerous stand-alone CD recorders make by Philips and available in the U.S. under the Marantz label.

High Resolution Bit Splitters

Prism makes a box that will let you convert the analog signal to digital at 96kHz 24 bits, and then split the signal up to record on multiple tracks of a DA-88 or ADAT machine. It takes six tracks of 16-bit storage to accommodate 96kHz of 24 bit data. When you play the data back, the box puts the bit stream back together and spits it out at the original 96kHz 24 bits.

Apogee uses a similar but incompatible method of bit splitting storage for high bit depth audio. Rane has a stand-alone box for bit splitting called the PaqRat. (Apogee uses the Rane format.) The Yamaha 02R digital console has a bit splitting method of storing 24 bit mixes that is not compatible with either the Prism or the PaqRat format.

These methods of splitting up the digital signal will work with any digital multi-track format. You could use a multi-track optical disc recorder, or a Digital Audio Workstation to store the split up digital audio. If a workstation is the preferred vehicle, long term storage can be on CD-R in CD-ROM format. Just dump it back into the workstation, convert it to whatever format you need, then spit it out as stereo audio.



Not Just Stereo Any More

Now I guess we have to talk about multi-channel mixes. How about all of those 5.1 remixes you are planning to do in your spare time? You are going to need somewhere to put them when you are done.

Prism makes another box that is designed to take the 5.1 channel 24 bit audio and squeeze it into eight tracks of 16 bit storage. DTS uses this method for storing mixes on DA-88 tapes. The tapes are then sent to DTS where they are encoded into the DTS bitstream. The DTS bitstream is then pressed into an audio CD or a DVD for consumer playback. If your final destination is Dolby Digital, you can mix to six discrete tracks and encode them yourself with SoftEncode. The final results can be stored as a stereo encoded signal for decoding upon playback.

I prefer keeping the original six tracks un-encoded in case I later decide I want to make my mixes available in multiple formats. You think Betamax and VHS made things confusing, wait until you have to sort out all of these new audio formats.

I realize that I have had to cut a few corners here to fit things in, (not much room here on the last page) but now you know that deciding on a final mix format is no easy task. If you choose just one format, it will probably be the wrong one, that is why I usually mix to three or four different formats simultaneously. If the DAT tape wrinkles, then I still have the CD. If the CD won’t play, then I still have the Optical disc. If everything fails, then don’t tell anyone that I was running a cassette.