The normal phase shift wrt frequency. This is rarely uniform across the frequency response of the preamp (or most other devices).
Yes. It's a mathematical function, and can be modelled fairly easily assuming one has the full specs of the components used ... including ESL
Electronics might disagree ...
Yes indeed and many instrumentation and measurement applications use this approach but for audio applications, almost all preamps/amplifiers which are DC coupled internally have some form of coupling capacitor on their input to prevent small DC offsets on the input signal being amplified into large DC offsets later on in the signal path which at best would lead to the likelihood of asymmetrical clipping and at worst would cause speaker voice coils to quickly burn out. Hence their frequency response doesn't usually extend as low as 0Hz.
Sure, there are a few exceptions ... my earlier, I did say "almost all"
Which makes them AC-coupled. As such, the LF phase varies in a predictable way that is determined by the cut-off frequency.
Can you determine the phase difference between the 100Hz and the 1kHz tones after they passed through this shelving high-pass filter?
So we agree the phase shifts at lower frequencies will differ from those at higher frequencies.
it's certainly measurable and can be calculated. In the above example, at 100Hz the phase shift's about 20 degrees and at 1Khz it's somewhere around 2 degrees.
try switching the wires on your mids so they're out of phase with your woofers ...
phase shift exhibited by signals of different frequencies on the same signal path is very much valid, as my two screen clips above demonstrate
Check this circuit.
You can't measure the phase difference between signals of different frequency.
Completely unrelated. Speakers are non-minimum-phase. The effects you hear are those due to combining two different paths.
Your screen demonstrates that signals of different frequencies are shifted by a different amount. I never questioned that.
Relative phase shift has no meaning.
There were quite a few around in the ‘70s. A lot of custom built were available here as well as off the shelf. Heavy too.
You should carefully read this article and related litterature. The effects of phase distotrion, i.e. phase response differing from minimum-phse behaviour, are audible by the way the peak factor changes and thus results in triggering non-linearities in the reproduction chain, including air compression and audition.
"Extremely low" is more than zero so it means the effect is perceptible. I have to say, my ears might not be able to specifically attribute any effect to phase distortion or even detect it in the first place but by changing the phase relationships of different frequencies, you will eventually change the tonal quality of the sound. Consider an open A string being plucked; the waveform generated is close to a sine wave. If that A string is mounted on a sound box, the tonal quality changes because some harmonics are at different levels although the fundamental note remains an A. Now think about a trumpet playing the same note, the sound heard and the waveform are quite different although the fundamental frequency is the same. I'm not suggesting phase distortion will make a harp sound like clarinet but slight changes in the phase-frequency relationship will inevitably alter tonal quality - i.e. phase distortion is audible to some people and by reducing it, we clean up the sound.
On the topic of “punch and smoothness differences” in preamps ...
