The development of surround sound formats has created more opportunities for the audio engineer to explore and exploit the sonic possibilities. But with the flexibility came technical problems and challenges. Fortunately, some of these issues are addressed by the Channel G Surround plug-in from McDSP. In this edition of Colin’s Corner I’ll discuss some of the features and operating tips on surround sound mixing and using the Channel G Surround plug-in.
For starters, the scope of this article is going to discuss the 5.1 surround format – left, right, center, left surround, right surround, and LFE channels (L, R, C, Ls, Rs, and LFE). The increased number of channels is intended to immerse the listener in an audio experience far superior to ‘just stereo’. A colleague of mine once said surround would be great, because now the consumer could have two speakers in the family room, one in the kitchen, a pair for the bedroom, and something for the cat to sleep on. Ok he was kidding, however his point was right on. The audio engineer (and hopefully the end consumer) needs to know what purpose each surround channel is intended. When mixing for surround, be it music, film, or gaming audio, the design of the surround format (how many channels, sub-woofers available, etc.) should be kept in mind as the mixing process unfolds.
Sticking with the 5.1 format, a typical mixing strategy is to have the ‘focus’ of the audio content in the L, R, and C channels. The Ls and Rs channels are used for ambient sounds and subtle (or not so subtle) panning effects to , you know, surround the listener in the audio experience. The LFE channel is what you use to annoy your neighbors, or at least give you something to pump the kick drum or low end of the explosions through.
While all this flexibility is great, maintaining balance in the mix is more difficult as audio cues, instruments, and effects are coming out of more channels. If only there was a way to divide the 5.1 channels into some sort of logic group of channel sets, and apply some sort of dynamic range and level control to each set. Gosh, that is just what the Channel G Surround Compressor/Limiter plug-in does, so read on!
Channel G Surround and Channel Sets
The Channel G Surround Compressor/Limiter is comprised of four individual compressor/limiters, arranged into four channel sets – LR, C, LsRs, and LFE. The LR, C, LsRs, and LFE channel set compressor/limiters can be linked to other channel set controls, and choose from any combination of the LR, C, LsRs, and LFE channels as their input key signal.
The channel set compressor/limiters in the Channel G Surround plug-in offer independent control – different threshold, ratio, knee, attack, release, and make up gain – for each of the LR, C, LsRs, and LFE channel sets. Each channel set compressor/limiter can be bypassed separately as well. These separate channel set control groups give the user the flexibility they need to properly mix surround format material. The channel set control linking improves workflow considerably.
For example, a user can apply hard knee and high ratio settings on the LR and C channel sets, while using more gentle ratios, attack, and release values for the LsRs channel set, and something else entirely for the LFE channel. In this case, each channel set compressor/limiter is using only its own inputs as the key signal for compression.
Channel Ducking / Automatic Mixing of Surround Channels
The real power of the Channel G Surround plug-in comes from its ability to allow each channel set compressor/limiter to key from any combination of channel sets. The LR, C, LsRs, and LFE channel sets are available as key inputs to all four channel set compressors for a variety of processing choices.
Consider this processing a 5.1 mix containing dialog in the center channel competing with the audio of the left and right channels. The LR channel set compressor/limiter selects the C channel as its input key signal, causing the levels of the LR channel set to drop when speech occurs in the C channel. The listener attention is drawn to the center where the dialog is occurring, and the other content in the LR channel set is no longer as much a distraction. This method of reducing the levels of one or more audio channels with another audio channel is often referred to as ‘ducking’.
The four screen shots below (example 1) show the LR, C, LsRs, and LFE channel set compressor pages in Channel G Surround. Each uses only their own input for compression, with the exception of the LR channel set compressor/limiter, which has selected the C channel.
Clearly in this example some judicious fader riding could also alleviate the problem. But the use of multi-channel ducking as only possible with the Channel G Surround plug-in is far easier to setup, most likely a sonic improvement, and is fail safe (no missed automation cues).
This process can be applied to any combination of channels. The C channel could duck the LR and LsRs channels. The LR channels could duck the LsRs channels. The LCR channels could duck the LsRs channels. You get the idea!
Channel Set Linking
While the independent control of each channel set compressor/limiter is great, at some point the relative control settings are made, and what remains is the adjustment of all channels concurrently. This is where channel set control linking comes in very handy.
Using the ‘master’ (M) and ‘linked’ (L) control buttons in the Control Matrix section of the Channel G Surround plug-in, a single channel set compressor/limiter can control all four channel set compressor/limiters. Usually the most ‘prominent’ channel set is used as the master, however groups of channel sets also work well together.
For example, suppose the LR and C channel set compressor/limiters have been setup appropriately. By linking their controls, now the balance of the LCR channels is controlled independently of the Ls, Rs, and LFE channels. The screen shot excerpt to the right shows this linking configuration (example 2).
In another example, suppose there is too much low end in the mix. The LFE channel can be made to operate independently of the LR, C, and LsRs channel sets and setup to control the offending low-end rumble. Meanwhile, the LR, C, and LsRs channel sets can be linked together once their relative balance is established, and workflow remains fast and simple. The screen shot excerpt to the right shows this linking configuration (example 3).
Channel G Surround – Not for Cats
Now that you’ve had a chance to digest my completely biased opinion about another McDSP product, give the Channel G Surround plug-in a try on your next surround project! The flexibility of surround is great, but only if you have an equally flexible compressor/limiter to control all the channel signal levels.