Search found 3705 matches

by JR.
Sun Mar 22, 2009 11:04 am
Forum: Pro Audio Design
Topic: A Discussion About True Power Summing for Stereo Compressors
Replies: 65
Views: 133060

Re: A Discussion About True Power Summing for Stereo Compressors

I will second that the math is valid. The SQRT in log domain is simply a scale factor (div/2). There are subtle errors in practice from not symmetrically performing the square root in actual device junctions, but this will only confuse the discussion, the error is surely modest. I really need to but...
by JR.
Sat Mar 21, 2009 2:32 pm
Forum: Pro Audio Design
Topic: A Discussion About True Power Summing for Stereo Compressors
Replies: 65
Views: 133060

Re: A Discussion About True Power Summing for Stereo Compressors

Regarding crest factor related errors, I am more familiar with errors associated with RMS circuitry saturating in the x^2 stage. Most RMS chips specify a maximum crest factor for this very reason. x^2, by logging and then multiplying by two, (squaring in the linear domain but expressed in the log d...
by JR.
Sat Mar 21, 2009 10:17 am
Forum: Pro Audio Design
Topic: A Discussion About True Power Summing for Stereo Compressors
Replies: 65
Views: 133060

Re: A Discussion About True Power Summing for Stereo Compressors

Yes I have been making Pk/VU meters for a few decades so familiar with crest factor. I even calibrate my meters in fixed dB steps so crest factor can be visually imputed from simple observation. Regarding crest factor related errors, I am more familiar with errors associated with RMS circuitry satur...
by JR.
Fri Mar 20, 2009 9:35 pm
Forum: Pro Audio Design
Topic: A Discussion About True Power Summing for Stereo Compressors
Replies: 65
Views: 133060

Re: A Discussion About True Power Summing for Stereo Compressors

Aren't we saying the same thing? Not exactly, John but close. Summing after detection, at least with rms, washes out coherence/incoherence altogether. It doesn't emphasize or de-emphasize those components. They just don't matter. I think I would agree to: "That said using "RMS" detec...
by JR.
Fri Mar 20, 2009 12:48 pm
Forum: Pro Audio Design
Topic: A Discussion About True Power Summing for Stereo Compressors
Replies: 65
Views: 133060

Re: A Discussion About True Power Summing for Stereo Compressors

Almost forgot to mention this.. Back when I got a decent 4 track, a Tascam reel to reel @ 15 IPS, I built a 4 channel version of JRs compander from the 1981 Popular Electronics article and used it blissfully ignorant of higher priced NR systems. Sounded very good and I was happy for a while... Then...
by JR.
Fri Mar 20, 2009 12:23 pm
Forum: Pro Audio Design
Topic: A Discussion About True Power Summing for Stereo Compressors
Replies: 65
Views: 133060

Re: A Discussion About True Power Summing for Stereo Compressors

That said using "RMS" detection (or IMO any rectification) before summing, will over report incoherent signals relative to coherent. Thanks for the discussion John. I agree with most everything else except the above. I believe the opposite of the above is true: Summing prior to rectificat...
by JR.
Fri Mar 20, 2009 9:54 am
Forum: Pro Audio Design
Topic: A Discussion About True Power Summing for Stereo Compressors
Replies: 65
Views: 133060

Re: A Discussion About True Power Summing for Stereo Compressors

Before I start ranting about RMS, lets not forget important rule #1 about audio.. If it sounds good, it is good. OK where to start. Regarding the sound of dynamics processing, we are basically multiplying an audio waveform by a control voltage. The spectral content of this control voltage can add ar...
by JR.
Thu Mar 19, 2009 10:14 pm
Forum: Pro Audio Design
Topic: A Discussion About True Power Summing for Stereo Compressors
Replies: 65
Views: 133060

Re: A Discussion About True Power Summing for Stereo Compressors

I'll chime in some more tomorrow.. I have been trying to decipher DBX's claims for RMS vs. simple average for decades. They were making claims about it impacting decode accuracy with their tape NR, back when that was a major business. I even recently did some work with RMS vs, Average detection in m...
by JR.
Sat Mar 14, 2009 7:34 pm
Forum: Pro Audio Design
Topic: OTB Mixer Using Current Summation
Replies: 137
Views: 214275

Re: OTB Mixer Using Current Summation

thanx and very cool.. let me know if any questions. or further discussion. There are several interrelated dependancies. While I'm not sure how to test completely in isolation. I have two questions about pan law.. A) is there a group consensus on nominal pot impedance? B) is my first try approach rea...
by JR.
Sat Mar 14, 2009 12:58 pm
Forum: Pro Audio Design
Topic: Active Summing mixer using THAT Ic's and some...
Replies: 24
Views: 42850

Re: Active Summing mixer using THAT Ic's and some...

Bingo...

If that opamp is driving the outside world perhaps add a 50-100 ohm resistor in series. Also good practice to use small cap in parallel with 100k feedback R with similar cap across R to G2 (for symmetry. I'd tune that RC for say 200 kHz or so (say 10pF).

JR