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Forums - Music techology
Subject: Phase(freqency) analysis
Viewing all 9 messages - View by pages of 10: 1
Original Message 1/9 31-Jan-07 @ 07:23 AM - Phase(freqency) analysis
After running some searches on google it seems this is not-so-obvious as I thought: I need a software analyser that reveals the phase characteristics of a VST (effect) plugin... well if there is such thing. (Well, I migth be able to build one for myself in Reaktor if everything else fails, but I guess that would take some time
)
Message 2/9 31-Jan-07 @ 10:55 AM - RE: Phase(freqency) analysis
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Message 4/9 31-Jan-07 @ 01:20 PM - RE: Phase(freqency) analysis
Message 5/9 31-Jan-07 @ 08:42 PM - RE: Phase(freqency) analysis
http://www.ymec.com/products/dssf3e/
free for 30 days, quality FFT, phase-frequency graph (between left and right channels) and a LOT more. And now the bad news: all DPS EQs with IIR filters cause phase distortion. There are DPS EQs with absolutely linear phase characteristics, but they introduce processing delay.
(Not that an analog EQ would be phase-transparent, no. They just suck differently
)
Message 7/9 02-Feb-07 @ 06:42 AM - RE: Phase(freqency) analysis
All I remembered from college days that all DSP algorythms are basically built of two basic blocks: signal amplifiers/attenuators and delay units. Now depending on how you combine these you can have a structure with feedback (IIR circuit) or without feedback (FIR circuit). IIR is called IIR because its reaction to an impulse is a decaying (or increasing) signal that will never reach 0 in amplitude (Infinite Impulse Response).
FIR on the other hand is a circuit without any feedback, and so its response in time for an impulse is finite. (Finite Impulse Response = FIR).
Now most of the circuits used in music production are IIR circuits, because FIR introduces processing delay. The downside of IIR is that circuits with feedback can produce an unstable signal, and also they introduce phase distortion. The kind of phase distortion introduced depends on the implementation (so the designer should preferably create a circuit thats phase distortion is somehow not-so-disturbing to the human hearing... I guess )
The point was that for some reason I assumed phase distortion is not something that you can hear (because you can't distinguish two sine waveforms which only differ in their phase), but obviously I was wrong. So it turned out that using a highpass filter on an effect bus does much more than "just removing some low end"...
As far as I have experienced, these days EQ's can sound really transparent despite I could measure their pghase distortion (to some degree: it wasn't a very accurate measurement though). Now I'm not so experienced with hardware EQ-s, so I guess their phase distortion is also considered "noticeable, but sounds all right"...
Message 8/9 02-Feb-07 @ 06:46 AM - RE: Phase(freqency) analysis
[image file]
On the left: frequency characteristics of the reference signal (pink noise) and the filtered signal
On the right: phase characteristics of the filtered signal
Message 9/9 02-Feb-07 @ 06:51 AM - RE: Phase(freqency) analysis
[image file]
Unprocessed and processed in one graph...
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