Compressor Attack Release Signature Comparisons

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Bruno2000
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Compressor Attack Release Signature Comparisons

Post by Bruno2000 »

I did some tests comparing the Attack and Release signatures of some of the compressors that we have that are favorites for voice. Here's the info on these tests: The test tone was generated by an Audio Precision System One, and recorded to Pro Tools at 96kHz through a 192 interface. 0 crossing for the burst was verified via Pro Tools waveform to be correct. The steady state 1kHz tone is at -6dBr (0dBr=1.228V RMS) for 1k5 cycles, then +4dBr for 500 cycles (10dB "burst"). All comp thresholds were set for below compression threshold with the lower level tone, and about 4dB compression (according to their meter) during the burst. Ratio on DBX165 was set at 6:1 (really about 4:1 according to my tests) and the Pico was set at 4:1 (also, according to my tests) for both the RMS and NLC (Auto) settings. The Manley's A/R settings were set for what most of the freelance engineers here use for vocals, and although no one here uses the Manley "Limit" setting for vocals, I ran the test anyway.

Enjoy!
Bruno2000

Editor: In order of appearance, input (blue) dbx 165 (green), Pico RMS (red), Pico Auto-NLC (dark blue), Manley Comp (dark green), Manley Limit (rust)...
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mediatechnology
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Re: Compressor Attack Release Signature Comparisons

Post by mediatechnology »

Thanks Bruno! I took the liberty of embedding the image.

Amazing how close the Pico RMS is to the dbx 165 and Manley Comp.
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JR.
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Re: Compressor Attack Release Signature Comparisons

Post by JR. »

Back when I was doing active development work on dynamics (comps, NR, etc) I made my own tone burst circuit, basically a variation on a gate, that switched on zero crossings, and had an adjustable amount of attenuation, as well as adjustable on/off duration. I either fed it with a sine wave to view representative scope traces, or program material to artificially increase the transient dynamics of a musical sample for listening tests. You can listen to sine wave bursts but it takes some training to learn what a good sine burst sounds like.

From observation only the last signal trace above (Manly?) shows evidence of clearly mishandling that transient step. This can be audible on dynamic musical program. All the other traces are mainly reflecting different attack and/or release times. I found when designing dynamics, that the ratio between on and off level matters a ton. The relatively small step is much easier to handle than a larger transient step.

I did a lot of work with cheaper IC gain elements so had to parse out and manage their shortcomings.

=========

I drew up a schematic after the last time I discussed this.
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I basically use a D type flip flop to force switch to occur not only on zero crossings, but on even number of zero crossings so it plays full cycles (it matters for DC content). a slow up/down ramp to set on/off time, and signal pass through for on/off level setting.

Note: this is not a schematic of my old working circuit since that was decades ago and long gone. This schematic is close but may have mistakes, but looks good as far as I can tell.

JR
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mediatechnology
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Re: Compressor Attack Release Signature Comparisons

Post by mediatechnology »

Roger - FWIW Your Krohn-Hite 1400 also does tone bursts. You have to jump the Ramp Out to Trigger Gate In BNCs.

John - You've motivated me to dig up the 8038 function generator I designed with tone burst. That might be fun to put, along with a copy of your schematic over in Document.
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JR.
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Re: Compressor Attack Release Signature Comparisons

Post by JR. »

One thing I found really useful was the ability to feed music through my burst gate... that way I could make random program material significantly more dynamic..

I was dealing with less stable gain cells (ne570/ne572), that could get all glitchy when hit with transients from low level... The modern stuff should and did look pretty well behaved.

That one limiter was a little squirrely but not unique... apparently some kind of a fast attack circuit that over reacts. I would look at a lot more combinations of on-level/off-level, and perhaps off-duration if dealing with very slow release times.

Enjoy... I spent way too many hours trying to make NR companders transparent and accurate. If you make a compressor too transparent some people might not like it...

JR
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