Surround Sound Mixing

It’s been almost five years now since I took the plunge and invested in a complete Dynaudio Air 5.1 surround sound monitor system. At the time, I though that Surround Sound on DVD-Audio and SACD discs was going to take off among music consumers. That didn’t really happen. Back then, I could walk into Tower Records or the Virgin Mega store in Union Square and find DVD-A discs from the likes of Seal or John Hiatt, but the last time I visited Virgin (Tower’s gone, as we all know) I had to talk to a whole bunch of store people before I found someone who even knew what DVD-A discs were, and how they differed from regular DVD-Video discs with music content on them. “Hmm, yeah, I think I do remember those. No one ever bought them.” These discs are still available on Amazon of course, but I doubt they sell in any large numbers.

With hindsight, there are a few obvious reasons for why these formats failed:

1. -The format war between SACD and DVD-A never got resolved. They’re both still around, but neither of them is doing well.
   

2. -Many consumers prefer downloads (mainly from the iTunes store) over physical discs, and there aren’t yet any widely used true HD quality consumer standards for surround downloads.
   

3. -No reasonable portable playback of HD surround material - True Surround Headphones are both very expensive and rare, and surround capable portable playback units even more so.
   

4. -No big installed base of capable playback equipment.
   

5. -The CPPM copy prevention system for DVD-A, and the fact that SACD does not use PCM Digital Audio but a completely different system that ordinary computers cannot play back - Why would consumers want to invest in a new technology that restricts making backup copies or moving audio between various playback units when CD’s aren’t restricted at all and the DVD-Video encryption was broken a long time ago? I think this is by far the biggest reason for failure. With these restrictions in place, CD’s and Video DVD’s provide a much more convenient experience.
   

6. -Competition from DTS-encoded CD’s and DVD’s - Even though DTS is a lossy format that do not have the same audio fidelity as the lossless or uncompressed formats of DVD-A and SACD, it still sounds quite good. And as most consumers are happy listening to MP3’s which is a similarly lossy format, getting the benefit of surround audio makes the trade off in audio fidelity worth it. DTS Surround Discs aren’t that popular either though, but at least there’s a reasonable niche market and DTS (the company) is still promoting them.
   

So even though the surround music market hasn’t been blooming, I’ve still been able to keep myself somewhat busy with surround for film and the occasional music project. I’ve also done surround mixes of a number of my own personal projects as well as provided free surround mixes to some of my regular stereo clients (who were still paying for the stereo mixes). I’ve also been doing a lot of research into development of new mixing techniques for surround, and I’ve done my best to stay updated on what everyone else is doing in this field.

Audio Philosophy

Disappointment

Before I purchased my own surround system, I’d hardly ever heard surround sound outside of movie theaters, so when I finally got my system all setup, I had a blast watching, and especially listening to, all three Lord Of The Ring DVD’s and many other big blockbuster action movies. Well mixed surround sound really is an amazing enhancement of the movie watching experience, and that elevated my already high expectations for surround music even further.

But after purchasing my first couple of DVD-Audio discs and dealing with the hours and hours of headache it took to figure out how to even play them back on my Mac, (To this day I can still only playback Dolby Digital and DTS streams through VLC and have to resort to obscure command-line DVD-A utilities running in Windows under VMWare Fusion to rip the CPPM protected Meridian Lossless Streams to hard disk) I was kind of disappointed about the whole experience. To put it simply, it basically seemed to me that most mixes could be put into one of two groups. Either they were very conservative or they were way too gimmicky.

The conservative mixes were basically just enhancements of the stereo experience with mostly ambience and just a little bit of everything else added in the rear channels, some vocals and a few  other elements added to the center channel, and that was about it. I could achieve similar results by simply sending a plain old stereo mix to both the front and rear channels. It “surrounds” you, but it doesn’t really bring you into the music. I had been expecting much more depth, clarity, and more of a feeling of envelopment.

The gimmicky mixes felt like the engineers had simply spread all the elements out between the different speakers. There’d be a guitar in the rear right speaker, a synth sound in the rear left, vocals exclusively in the center channel, tons of bass and kick in the sub channel and so on. Then you’d have pan moves where the guitar solo would move from the front to the back or spin around you. Kind of cool, and it worked decently for some styles of music, but I wouldn’t call it tasteful.

It felt like there was a big potential for beautiful, clear and enveloping sound that just wasn’t being realized. And so I set out to try and create better sounding surround mixes.

Recording and Mixing in Stereo

There are many different ways of creating a stereo mix. For example, when mixing multiple mono sources, such as recordings of an electric guitar, an electric bass, a saxophone and a vocalist, done with one microphone each, they can be panned across the stereo image through the use of the pan knobs found on all mixing consoles and in all DAW:s. The pan knob divides the signal between the two speakers. Turn the know to the left and it will send more of the signal to the left speaker and less to the right, resulting in our ears interpreting the sound as if it originated somewhere to the left of center.

Another way to achieve a similar result is through the use of delay. With a real acoustic sound, such as someone clapping their hands in front of someone else, but a little to the left, the sound waves reach the person’s left ear slightly before they reach his right ear as the distance from the source to the right ear is longer than to the left. To achieve a similar effect while mixing in stereo, the engineer will delay the signal being sent to the right ear slightly, and the result will be that the listener “hears” the sound coming more from the left. There are limits to how much delay can be used though, because at a certain point, we start distinguishing the two signals as separate signals instead.

True stereo recordings, done with multiple microphones, take advantage of one or both of these effects during the recording. One example is placing a pair of microphones in front of an orchestra in a so called “ORTF” -configuration - French radio people at the “Office de Radiodiffusion Television Francaise” came up with this approach in the 1960’s, trying to mimic how human ears work. Two cardioid microphones are spaced apart about 7 inches, (approximating the distance between human ears) and aimed away from each other at a 110 degree angle, allowing engineers to take advantage of both arrival time differences and the volume differences between the microphones’ on and off axis response.

Another example, that only takes advantage of volume differences, is the X/Y stereo configuration, involving two microphones placed extremely close together (eliminating arrival time differences) but aimed away from each other at a 90 degree angle. This approach gives a fairly realistic stereo image while still maintaining good mono compatibility. (Summing a stere image that includes arrival time differences, whether recorded that way or created with delay during mixing, can often lead to undesirable effects such as comb filtering and loss of sound at certain frequencies.) Additional stereo recording techniques include M/S and Blumlein.

Over all, I would say that stereo recording techniques definitely provide more realistic sounding results than stereo images created during mixing with the above mentioned techniques. However, what works best in any given situation is of course completely at the discretion of the engineer and will depend on his or her artistic goals.

Mixing In Surround

Now what about surround? Obviously, the panning of mono sources in a surround mixing environment works very similarly to the way it works in stereo. It gets more complex of course, as the panner has to divide signals between more speakers, and you now have a three dimensional sound field with both x and y axels, rather than just a simple two dimensional field between left and right. The panning via delay technique works too of course, and naturally, the two can be combined.

There are issues with mixing this way though. Since the same signal gets sent to many speakers (which is what happens with the surround panners built into most DAW software and Digital Consoles capable of surround mixing) the location of the listener becomes very important. Unless he or she stays exactly in the center of the surround field, you’re going to end up with arrival time differences between the signals originating from the different speakers. And this time, these are not intentional differences, decided upon by the engineer, but rather, they depend upon the listener’s location which, of course, the engineer cannot control, resulting in your pan positions changing as the listener moves his head. And as you have more speakers reproducing the same signal, you’ll get more comb filtering effects, and ultimately a more cluttered and less clean sound.

But how about true surround recording techniques equivalent to the X/Y and ORTF methods used for stereo? Yes - There are a number of surround recording techniques in use, most of them based on, or extensions of, existing stereo recording techniques. The limiting factor with these methods however, is that the panning position for audio sources largely gets decided by how they were placed in the space where the recording took place. Sure, levels sent to the different surround speakers can be tweaked and manipulated during mixing, but only so much, because at some point, where the level gets too low or too high in some of the speakers, you loose the realistic feeling of the original recording, which defeats the purpose of having recorded that way in the first place.

MSS - Multi Stereo Surround

With all of these issues and potential problems in mind, I developed a simple mixing method that can help achieve better results. I’ve decided to call it MSS, or Multi Stereo Surround, as the

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email: mix@unne.net