# Digital compression causing feedback



## Subby (Oct 28, 2011)

Hi everyone. I'm working a show right now running a Yamaha 01V96 digital board with onboard (digital) compression. I'm working on dialing in the gain lineups for the wireless mics we are using (Sennheisers EW100 G2 with ME2 elements, which are not my favorite elements). However, when I apply the compression to one of the actors' mics, I get feedback and I don't fully understand why.

First, the compression settings:
Ratio - 4:1
Attach - 50 ms
Release - 100+ ms
Knee - 2-3
Gain - 0 dB
Threshold - various levels.

The process I go thru in setting up the gain lineup for a mic is I have then actor come on stage, sing full voice so I can set the head amp level to just below clipping. I then ask them to give me their softest point in the show whereby I set the fader level on the board. At this point I may have them stand quietly while I listen on the headphones and set the noise gate/expander. Next, I have them give me their loudest volume and I turn down the THRESHOLD level until I get the level I want.

What's happening with this digital board is, as I lower the threshold and engage the compressor, i.e. the gain reduction meters show gain reduction starting to kick in, I suddenly get a lot of feedback. I turn off the compressor, and it goes away.

I know I can raise the softer levels of the signal where feedback might be lurking, BUT ONLY IF I ADD GAIN TO THE LINEUP, which I am not doing with the compressor (GAIN = 0 dB).

I also know if the attack time is too fast I can cause distortion/harmonics, which could trigger feedback.

The only thing I can think of is to increase the ATTACK TIME to avoid generating distortion? Or maybe use the GAIN control to add some attenuation to the post-compressed signal??

Any suggestions in my setup and/or procedure? Anyone else have troubles with digital compressors?

Subby


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## Stookeybrd (Oct 28, 2011)

Is the feedback instantaneous or does it build up?

Double check your routing in the console. Make sure that you haven't assigned anything to an aux that is returning to the console or that something from another show isn't still programmed in.


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## DaveySimps (Oct 28, 2011)

I use digital compressors all of the time, and have had no issues, ever. I second the thought of checking your routing. If you want to email me a copy of your Studio Manager file, I am happy to look at it. Often time an outside set of eyes can catch something you might be missing. 

~Dave


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## WooferHound (Oct 28, 2011)

A compressor controls the volume.
If you have a vocal that is being compressed then the volume of the vocal is being reduced.
while the vocal is performing you may in fact turn up the volume so you can hear it better.
Whenever the vocalist stops, the compressor will release which is when it raises the volume back up to it's uncompressed setting.
That is probably where you are getting the feedback from.


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## avare (Oct 31, 2011)

WooferHound said:


> A compressor controls the volume.
> If you have a vocal that is being compressed then the volume of the vocal is being reduced.
> while the vocal is performing you may in fact turn up the volume so you can hear it better.
> Whenever the vocalist stops, the compressor will release which is when it raises the volume back up to it's uncompressed setting.
> That is probably where you are getting the feedback from.


I usually do not like short posts with large quotes, but it fits perfectly his time. Any compressor set wrong will do exactly what WooferHound wrote.

Andre


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## Subby (Nov 1, 2011)

@WooferHound & avare: I agree, except the feedback was hitting when I reduced the threshold without turning up the gain elsewhere, that's why its so confusing.

@Dave, I may send you a Studio Manager file if things persists.

To all - I think I found what might be going on. The compressor I pulled out of the Yamaha 01V96's library was one of the COMPANDERS. What I think happen is that as I turned down the Threshold control to engage the compressor, the noise expander section, that had scrolled off the screen, released because I did not simultaneously narrow the Width parameter. So all the feedback hiding in the noise floor was allowed thru.

Now, I need to test this theory this weekend when I get back. This makes sense if the performer was not singing, but if they were, as I thought they were, the noise expansion would have been open already.

Subby


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## waynehoskins (Nov 1, 2011)

Aha, compander. That's the problem. If it's like the compander in the O3D, it doesn't have enough knobs, you can't really set the expander and the compressor separately as you'd want to. I tried to use those once (the O3D has only one dynamics slot per channel, and I wanted both expanders and compressors) but they didn't do what I wanted. I ended up just going with straight compressors and was much happier.


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## museav (Nov 1, 2011)

Subby said:


> The process I go thru in setting up the gain lineup for a mic is I have then actor come on stage, sing full voice so I can set the head amp level to just below clipping. I then ask them to give me their softest point in the show whereby I set the fader level on the board. At this point I may have them stand quietly while I listen on the headphones and set the noise gate/expander. Next, I have them give me their loudest volume and I turn down the THRESHOLD level until I get the level I want.


Glad you seem to have found the problem but it should be noted that in general using compressors as a volume control is not recommended. If you want to use a compressor to control the dynamics of a source, say so you can increase the average level of a source without the peaks increasing as much, that is one thing but don't use it as a volume control.

Perhaps also relevant is that this is one area the flexibility of the 01V96 can potentially make you have to think a bit more. Along with the analog preamp trim/gain there is also a digital attenuator for each channel that is located after the gate and first insert point but before the EQ. You can also assign whether the channel metering is looking at the signal before anything other than the polarity switch, after all processing but pre-fader, or post-fader. And the 01V96 allows three options for where a compressor is inserted; post gate and pre-digital attenuator/EQ/fader, post-EQ and pre-delay/fader, or post-fader. All of these can interact as far as how the compressor works, what the channel metering is actually showing and how settings of the processors, attenuator and fader may affect one another.


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