Multi band compression/expansion

Discussion in 'Tracking / Mixing / Editing' started by CharlesDayton, Jul 12, 2006.

  1. CharlesDayton

    CharlesDayton Active Member

    I need a primer on multi band compression/expansion. I have heard it is good for removing unwanted reflections from dialog recordings, but I'm a little muzzy on the hows and whys. Any insight would be appreciated.
  2. RemyRAD

    RemyRAD Guest

    Charles, you should look into a used Dolby 361 unit? In that box, you have 4 bands of compression/expansion. If you can get the optional spectral controller, which are hard to come by, adjustments are much easier than going into the multitude of adjustments on the internal circuit boards. So when adjusted for voice, each band will compress above a certain threshold and below that threshold will begin to downward expand. So since it is spectrally processed, the downward expansion in the frequency bands that are below the threshold will help to eliminate certain audible reflections, noise and other artifacts in the acoustical space.

    You may also want to go to the Orban and/or CRL site as they have been doing multiband compression and expansion for broadcast processors since the 1970s.

    Spectrally stressed
    Ms. Remy Ann David
  3. CharlesDayton

    CharlesDayton Active Member

    I knew I could count on you Remy. I have the Waves C4 multi band comp/expander, and the L3. I was more looking for a tutorial on how it works. I have a pretty clear understanding of compression, not as clear on expansion(like how different is it from a slow gate, or a slo gin fizz for that matter)? And how does deviding these functions by bandwith work? It's funny, after 15 years in this business, I still feel like I'm only just getting the basics down.
  4. RemyRAD

    RemyRAD Guest

    Charles, sorry it's taken me a few days to respond. I've been a little busy at Voice Of America television lately, doing really terrible sounding talking head news/interview shows.

    The multi-band compressors that feature a gain reduction hold and then downward expansion help to clean up background grunge in their respective frequency bands when the threshold levels had been set to function when there is limited information in that frequency band. So when dealing with voiceovers and music, low-frequency noise and high-frequency white noise are reduced in addition to mid-band noise when the mid-band threshold, dropped below your preset level, while also yielding a dynamically equalized and compressed signal.

    DBX made a box called the 3BX which was a 3 band, linear downward expander. They marketed it as a dynamic range enhancer. But if you did not push it too hard (1:1.5) and followed it with a limiter, it would clean up a lot of background trash by approximately 10 DB, while you limited the dynamic range and since it was a multiband unit, it was not so egregious sounding. I know I have one of those old things still lying around somewhere? I can't remember the last time I used it? The CBS VolumeMax transmitter processor did something similar when used as the last stage prior to the transmitter input, as did the later series of Orban "OptiMods" did/do.

    Opti-MOD SQUAD
    Ms. Remy Ann David
  5. TVPostSound

    TVPostSound Guest

    That would be the Dolby CAT 43, 2 just sold on eBay this morning, from "Intersound" which has recently closed its doors.
  6. CharlesDayton

    CharlesDayton Active Member

    I have the Dolby Cat.43A. It's a great tool. Remy, thanks for the reply. So its acting like a frequency dependent gate? When a particular freq falls below your threshold level it attenuates that signal. I hope I'm not being dense here.
  7. RemyRAD

    RemyRAD Guest

    Xactly! I am also trying to chase down the external spectral controller option that I mention since I don't remember its specific part number? I found it to be a very interesting single ended vocal processor. Since I have 3 old used A361 units lying around, I too have been on the prowl for the external spectral controller. I'm now awaiting a reply from Dolby laboratories since I've stepped up my search for this ancillary item.

    Dolby on my brain
    Ms. Remy Ann David

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