[Mike Rivers]

On 9/3/2017 9:55 PM, James Price wrote:
As soon as you sum two signals where one was processed with EQ, the
phase relationship changes, doesn't it? I'm not talking about a pure sine
wave but rather a complex signal.

That depends on the signals and the type of equalization.

For instance, if you add a .5ms delay
to a sound, won't 1k, 3k, 5k, and 7k be 180 degrees out of phase whereas
2k, 4k, 6k and 8k will still be in phase?

If you finish the sentence. Those frequencies in the delayed version of the signal will be 180 degrees out of phase with those frequencies in the unprocessed signal. A single signal isn't "out of phase" unless you state what it's out of phase with. Oh, and any other frequency will be some amount of out of phase with its undelayed counterpart.

How you use those two versions of a signal determines whether or not you have an audio problem - or fix a problem - or create a desirable effect.


Doesn't using a compressor for
color add overtones?

Yes. That's what "color" is.


What happens to the phase between the altered and
unaltered material?

It depends on how long it takes for the signal to pass from the input to the output of the compressor. With an analog compressor, which has essentially no throughput delay, there will be no cancellation when the compressed and uncompressed signals are mixed. This is why "parallel compression" became a popular technique before we had DAWs and plug-ins.

On the other hand, if the compressor introduces a delay, then, when you sum its output with the uncompressed signal, either you'll get some phase cancellation (typically called "comb filtering").

From what I understand linear phase EQ's do keep phase in check, but have other undesirable issues.

A linear phase filter doesn't really exist in the analog world (there are some squirrelly exceptions so don't get all "what about..." with me). It's a product of digital filtering, which is based on delays. Linear phase equalizers can introduce several hundred samples of delay.

As for latency, I've heard that a lot of plugins report none, but there's still a change. Ever checked it with a test tone?

All plug-ins that affect the signal cause some delay. Some introduce a negligible amount of delay and don't affect musical timing, or, when combined with an unprocessed version of the same signal, only introduce significant comb filtering at high frequencies, or, for a small enough delay, outside of the audio range.

Some plug-ins report a theoretical amount of latency, through the audio driver, based on the number of calculations that it's doing. It's up to the DAW program to interpret that information and do something with it. Some do a better job than others. And of course if there's no latency reported, there's no compensation.

Nothing in digital audio "just works" all the time, on all systems. Whenever you introduce some processing in the signal path, you need to listen and decide if you've made the sound better or worse.