"Anthony Airon Oetzmann" airon@gmx.net wrote:
David, you wrote:
I have a question though, how does the gradual attenuation work? How about something that clips yet isn't continuous, like a cymbal crash? And are all those graduations for the setting necessary? I think instead of this, a self-adjusting attenuation would be even better. It should work at an aggressive level however, and step back or un-attenuate as soon as the clipping stops. What I'm thinking is something like the concept of variable bitrate MP3 encoding. When the decoder sees the first instance of a clipped sample, it automatically attenuates the full level, but after so many samples of no clipping, it steps back to no attenuation. And so on. What I fear is that a large spike could occur in the beginning or middle of a file, setting a high attenuation level, and then muffling the rest of the song which might not clip at all.
What you're describing is a Limiter. It would indeed be neat to have this function.
Of course this should be a lookahead limiter. The Ultramaximizer L1 by Waves looks ahead by up to 68 samples on a Protools TDM system(that's its processing latency anyway). I don't think having a second latency i our case would be all that bad. Problem is, who can write a Limiter like that ? Perhaps one the authors of a free VST plugin would include his Limiter code in here. For short peaks this would be the right thing.
Are there any papers or web sites that discuss the pros/cons of limiters? I have always had the impression limiters are undesirable because of the continuous fluctuation of the output signal level.
The way attenuation is currently implemented in the MAD plug-in, doing any kind of look-ahead is unfortunately promblematic. This could be changed, but the primary benefit of the current method is that attenuation changes are less audible than they would be otherwise.
-rob
Rob Leslie wrote:
"Anthony Airon Oetzmann" airon@gmx.net wrote:
David, you wrote:
I think instead of this, a self-adjusting attenuation would be even better. It should work at an aggressive level however, and step back or un-attenuate as soon as the clipping stops. What I'm thinking is something like the concept of variable bitrate MP3 encoding. When the decoder sees the first instance of a clipped sample, it automatically attenuates the full level, but after so many samples of no clipping, it steps back to no attenuation. And so on. What I fear is that a large spike could occur in the beginning or middle of a file, setting a high attenuation level, and then muffling the rest of the song which might not clip at all.
What you're describing is a Limiter. It would indeed be neat to have this function.
Of course this should be a lookahead limiter. The Ultramaximizer L1 by Waves looks ahead by up to 68 samples on a Protools TDM system(that's its processing latency anyway). I don't think having a second latency i our case would be all that bad. Problem is, who can write a Limiter like that ? Perhaps one the authors of a free VST plugin would include his Limiter code in here. For short peaks this would be the right thing.
Are there any papers or web sites that discuss the pros/cons of limiters? I have always had the impression limiters are undesirable because of the continuous fluctuation of the output signal level.
The way attenuation is currently implemented in the MAD plug-in, doing any kind of look-ahead is unfortunately promblematic. This could be changed, but the primary benefit of the current method is that attenuation changes are less audible than they would be otherwise.
I may have described a limiter, but I didn't intend to. I wasn't thinking anything along the lines of looking ahead either. I think something very easy to implement would be to just reset the attenuation setting after X samples of no clipping. This would of course increase the number of overall clips that "get past" the decoder, but would avoid the problem of a peak that sets an attenuation too large for the entire file. How would this be more audible, as I can keep setting and resetting the attenuation manually with no hiccups? Am I making sense?
-naw
On Fri, 15 Dec 2000 05:35:32 -0600, David Shin wrote:
I may have described a limiter, but I didn't intend to. I wasn't thinking anything along the lines of looking ahead either. I think something very easy to implement would be to just reset the attenuation setting after X samples of no clipping. This would of course increase the number of overall clips that "get past" the decoder, but would avoid the problem of a peak that sets an attenuation too large for the entire file. How would this be more audible, as I can keep setting and resetting the attenuation manually with no hiccups? Am I making sense?
This is the release parameter of a compressor/limiter. www.prorec.com has some nice info on compressors and other dynamic processors.
The difference is with a limiter(good one) you won't get clips and won't pull back the material too much. Since we see only a few nasty peaks and only very little sustained clipping, I suppose setting a base attenuation to -0.5 dB and having an optional limiter cut away anything else that pops up by more than 0.3 dB will ensure a nice smooth transient. I do urge you to check out a few compressors so you know what happens when a limiter starts going to work and how the transients look when it's done.
Tony
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Anthony Airon Oetzmann -
David Shin -
Rob Leslie