Surround Sound Mixing
It’s been seven years now since I took the plunge and invested in a complete Dynaudio Air 5.1 surround sound monitor system. At the time, I thought that Surround Sound on DVD-Audio and SACD discs was going to take off among music consumers. That didn’t really happen. At the time, I could walk into a Tower Records Store 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, I had to talk to a whole bunch of store people before I found someone who even knew what a DVD-Audio disc was, 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.” Now Tower Records is no more, and the Virgin Mega store in Union Square that I used to visit has been closed for a few years. These discs are still available on Amazon of course, but I doubt they sell in any large numbers.
Looking back, there were a few obvious reasons for why these formats failed:
- The format war between SACD and DVD-A never got resolved. They’re both still around, but neither of them is doing well.
- The majority of music consumers have slowly been shifting to downloads (mainly from the iTunes store) and streaming services like Spotify, neither of which offers music in surround sound.
- 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.
- No big installed base of capable playback equipment.
- 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.
- 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.
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 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 knob 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 you, but a little to the left, the sound waves reach your left ear slightly before they reach your right since the distance from the source to the right ear is greater than the distance to the left. To achieve a similar effect while mixing in stereo, you can delay the signal being sent to the right speaker 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. This technique also always causes phase issues to some degree
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 stereo 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 an x and a y-axel, 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. 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 new mixing method that can help achieve better results. A good friend of mine came up with a name for it: MSS, for Multi Stereo Surround, since the technique involves creating multiple stereo images between the various surround speakers. Recording in stereo using the previously mentioned techniques gives excellent results, and unlike their surround equivalents, they are not very complicated to setup. Using two microphones for a piano, drum overheads, and acoustic guitars etc, is very common, and most recording engineers are already doing it. Additionally, both plugin and external reverb and delay effects all output their results in stereo.
So my technique is basically to “create” multiple virtual stereo pairs between all the speakers. In a standard 5.1 channel surround system (leaving the subwoofer channel out of the equation since it is only use for very low frequencies) there are a total of 10 possible stereo pairs:
Image to come…
This means that you can have 10 stereo sources playing between 10 different speaker pairs (and therefore not competing with each other very much) theoretically resulting in very clean and spacious sounding results.
For example, I could mix a simple jazz recording the following way:
Piano (recorded with an ORTF Stereo Array) – The left mic hard panned to the left rear speaker and the right mic hard panned to the center speaker.
The piano is also sending to a stereo reverb effect with its stereo output panned so that the left channel is hard panned to the left front speaker and its right channel to the right rear speaker.
I really like the kind of sound this creates. It’s definitely not a realistic sound in the true meaning of the word, but having the close miked piano come from two speakers while having the ambience of it coming from two other speakers in different locations does create a very clear, enveloping, and, arguably, “natural sound.”
Then I’d do something similar with the drums, having the overhead stereo pair between the left front and the right rear, with the reverb from them between the left rear and right front speakers. The mono kick and snare mics can be left panned in the center between the left and right front speakers, with some being sent to the center speaker as well. And the snare would be sent to a reverb returning on the left and right rear speakers.
Acoustic bass (which was recorded in mono) I’d pan between the center and right front speaker while also sending it to a stereo reverb returning to the left rear and left front speakers.
The vocals could be kept more towards the middle, so they could be both between the left and right front speakers AND in the center speaker. A tiny touch of reverb in those three speakers too, but more reverb sent to the left and right rear speakers.
Finally, the saxophone can go almost in the same place as the bass, (since those two instruments occupy quite different frequencies and hardly compete with each other) between the Center and Right Speakers. Putting the piano where I did kind of tilts the whole mix towards the left, so this helps compensate for that. I’d also send some of the saxophone to a simple short delay, imitating a natural slap back, panned between the Left Surround and Left Speakers. Then, finally send some more saxophone to a reverb returning to the left front and right rear peakers.
Take a listen for yourself!
In case this all sounds a bit too abstract, the mix I described above is a real song that I did mix that way, and you can download it right here and check it out for yourself.
However, since online distribution of Surround Sound content is still in its infancy, it’s not as easy as I’d like it to be. Apart from the obvious basic requirement of you, the listener, actually having a surround sound playback system, there are three different ways for you to get the content from my server to your ears, and the way that is best for you depends on what kind of equipment you own and how it is setup.
You can download the file right here: My Little Brown Book DTS.wav
CAUTION! Just right-click on the link (or ctrl-click if you’re stuck with only one mouse button) and choose “Save As,” “Save Target As,” “Download Linked File” or something like that. DO NOT just left-click on the file as your browser might try to play it back directly, which could cause a lot of loud noise to come out of your speakers.
But downloading the file is only the first step. Now you have to decide how to play it back. And just like when you were downloading the file, DO NOT just double click on it since doing so could cause a lot of noise to come out of your speakers. That’s because this file is encoded in DTS format.
Now, the three ways of playing this file back:
- You own a multichannel sound card for your computer that outputs each channel (Left, Right, Center, LFE, Left Rear and Right Rear on separate analog output connectors, hooked up to either six analog inputs on an amplifier or directly to each self-amplified or ”powered” speaker.If this is the case, all you need to do is download the free (as in both beer and freedom) media player VLC and configure it to work with the surround outputs of your sound card.
- Your computer has either an optical or a coaxial digital audio output (spdif) connector, and you have it connected to a receiver with the appropriate input, and that receiver has a DTS logo on it.If this is the case, you should be able to play back the file through any media player software, such as iTunes, Quicktime, Microsoft Media Player, Winamp, etc. If you still only receive noise, it might be that you have to enable something like “Bitstream Passthrough,” “DTS Passthrough,” “Dolby Digital Passthrough,” or “Spdif Passthrough,” either in your playback software, your sound card settings, or both.
- You own a CD or DVD Player with the same kinds of digital audio outputs I described earlier, and you have it connected to a receiver with a DTS logo on it.If this is the case, just burn the file onto a CD with any burning software (Toast, iTunes, Easy CD-Creator, etc) and you should be able to play it back on your system. Just be sure you make a regular Audio CD and not an mp3 or data CD or something like that.