The holiday record that I’m preparing for iTrax was recorded Shawn Murphy at 96 kHz/24-bits. He mixed the project to stereo at 88.2 and then downconverted to 44.1 for the CDs. The mastering was done on the 44.1 CD version. Then he mixed the project in 5.1 at 96 kHz/24-bits. It was also mastered and transferred to a hard drive. It’s been waiting for someone to offer it as a download and Jim Self, the producer of the project, found me. But I want to offer it at 96 kHz/24-bits in stereo as well…or at least at 88.2 kHz/24-bits.
Jim checked with Shawn and was told that there isn’t a high-resolution stereo mix. So I have to create one. The options are as follows: go back to the original Pro Tools multitrack masters and remix the project to stereo at 96 kHz/24-bits. This would open up a whole can of worms…matching the CD mix, artistic choices, additional costs, and the mastering would have to be redone. Another choice would be to upsample the 44.1 mastered CD into a high-resolution version. This happens more than you might imagine and despite what others may tell you it’s a completely useless exercise. The fidelity doesn’t change after the original recording. The third and final method would be to downmix the 5.1 masters into stereo. That’s the road we’ve decided to go down.
What is downmixing? It’s the process of taking a multichannel track and creating a stereo (or mono) version of the that track by reallocating the CENTER, LEFT and RIGHT SURROUND and LFE channels to either the LEFT or RIGHT FRONT channels. It’s a process that happens all the time in your optical disc player. When I prepare a project for commercial release, I have to include downmix “coefficients” for the Dolby encoded audio just in case the 5.1 mix has to be played back through a 2-channel stereo system. Once these coefficients are dialed into the metadata of the associated file, the player will automatically detect them and mix and distribute the audio channels according to these parameters.
The CENTER channel won’t have a center speaker in a stereo rig, so it get equally divided and sent to the LEFT and RIGHT FRONT speakers. But because it’s now coming out of two channels instead of a single speaker, the level has to be attenuated by 3 dB. The 3 dB drop is necessary to keep the perceived volume the same. This attenuation is built in to traditional PAN POTs on recording consoles as well…we want the same volume as we pan a signal between the left and right. The LEFT and RIGHT SURROUND channels are reduced by about 10 dB and combined in to the corresponding LEFT or RIGHT FRONT channel. And finally, the LFE is sent to the stereo channels and attenuated by a few dB. These parameters are adjusted to personal taste. The amount of information in the LEFT and RIGHT SURROUNDs does affect how much you want directed to the front channels but the numbers I’ve mentioned are pretty typical.
So that’s what I’m doing to the tracks of the “Tis The Season TUBA Jolly” project. The stereo mix will be exactly the same timbre as the 5.1 surround mix and maintain the same balance of instruments. And I get to hum along with my favorite Christmas music once again.