| phase distortion [message #197584] |
Wed, 08 November 2006 15:01  |
maxdimario
Messages: 3811
Registered: December 2004 |
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I've mentioned this directly and indirectly in the past.
I don't believe there is enough working knowledge around regarding the issue of phase distortion..
I am not talking about phase shift, nor being out-of-phase.
the issue of phase DISTORTION is probably one of the biggest and most misuderstood issues in pro audio recording..
anyone wish to comment?
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| Re: phase distortion [message #197604 is a reply to message #197584 ] |
Wed, 08 November 2006 16:32  |
Andy Peters
Messages: 1093
Registered: April 2004
Location: Tucson, AZ |
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| maxdimario wrote on Wed, 08 November 2006 14:01 |
the issue of phase DISTORTION is probably one of the biggest and most misuderstood issues in pro audio recording..
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You're right; most people don't know what they're talking about.
-a
"On the Internet, nobody can hear you mix a band."
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| Re: phase distortion [message #197796 is a reply to message #197784 ] |
Thu, 09 November 2006 14:57 |
 Bill Mueller
Messages: 4123
Registered: April 2004
Location: Joppatowne Maryland |
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I understood this to mean in-circuit, progressive phase shift. As in, all analog equalizers introduce phase shift as a function of their operation. Some, not all transformers introduce linear (same at all frequencies) phase/time shift, but all analog equalizers inject frequency selective phase shift (delay). Early A to D circuits (Sony Dash as an example) introduced hundreds or thousands of degrees of frequency selective phase shift. Until fairly recently (five to ten years?) phase shift (even frequency selective phase shift) was considered imperceptible. That was actually because the loudspeakers we were using to judge their perceptibility introduced so much phase shift of their own, they masked the in-circuit anomalies.
But of course, I could be completely wrong.
Best Regards,
Bill
"Don't take it personally. But this shit is a science." J.J.Blair
“The Internet is only a means of communication,” he wrote. “It is not an amorphous extraterrestrial body with an entitlement to norms that run counter to the fundamental principles of human rights. There is nothing in the criminal or civil law which legalizes that which is otherwise illegal simply because the transaction takes place over the Internet.” Irish judge, Peter Charleton
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| Re: phase distortion [message #197834 is a reply to message #197584 ] |
Thu, 09 November 2006 16:57 |
maxdimario
Messages: 3811
Registered: December 2004 |
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| Quote: |
phase distortion: Distortion that occurs when (a) the phase-frequency characteristic is not linear over the frequency range of interest, i.e., the phase shift introduced by a circuit or device is not directly proportional to frequency, or (b) the zero-frequency intercept of the phase-frequency characteristic is not 0 or an integral multiple of 2 radians. Synonym phase-frequency distortion.
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the above definition mentions that when phase shift is not directly proportional to frequency this is called phase distortion.
in nature high and low frequencies can shift in phase predictably through travel in air or when reflecting off surfaces.
when the phase shift is non-linear frequency wise you have an erratic re-distribution of the sound's energy.
usually this kind of distortion can be found in the worst sounding audio gear, regardless of specs
if you think about it any circuit that would cause phase distortion HAS to be 'wrong' from an audio perspective.
absence of phase distortion (not phase shift) translates in good audio.
one of the worst effects of phase distortion is the effect it has on impulse reproduction.
a clean crest of a 'transient' waveform can be distorted out of recognition.
phase distortion is also unpleasant and grainy sounding..
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| Re: phase distortion [message #197917 is a reply to message #197584 ] |
Fri, 10 November 2006 04:37 |
maxdimario
Messages: 3811
Registered: December 2004 |
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some eq's are much worse than others.
phase directly proportional to frequency?
you mean phase SHIFT proportional to freq? It's not 'just a delay'.
what happens is that DIFFERENT frequency components shift in time... either predictably and linearly as in phase SHIFT, or erratically and abruptly as in phase DISTORTION.
phase shift is a naturally occurring kind of distortion, phase distortion is not.
circuits which have high phase distortion are unmusical and should not be used for audio if given a choice..ever.
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| Re: phase distortion [message #198053 is a reply to message #197584 ] |
Fri, 10 November 2006 15:36 |
maxdimario
Messages: 3811
Registered: December 2004 |
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phase shift:
the harmonic content of a given sound is not reproduced correctly in time but the high harmonics arrive at a different point in time.
phase shift due to capacitance, mass of diaphragm in transducers, positioning of high/low freq drivers etc.
phase shift which is not linear in freq, such as poor eq circuits, negative-feedback-compensated circuits, Digital repro, sound going through resonators...both acoustic or electronic. is evil phase distortion.
there are plenty of guilty offenders out there with lovely specs and shitty phase distortion... proof of the low budget engineering involved..
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| Re: phase distortion [message #198054 is a reply to message #197995 ] |
Fri, 10 November 2006 15:40 |
Bill Mueller
Messages: 4123
Registered: April 2004
Location: Joppatowne Maryland |
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Ethan,
While I am not going to run wild with audiohypochondria, I will say that non linear phase delay is perceptible and there are even a huge number of audio devices (Aphex Audio Exciter and all of it's clones) designed to directly address these perceptions.
Especially in speaker topology, phase delays above the crossover frequency cause masking and smearing, typically leading to engineers pushing higher high frequency gain and achieving a harsh mix. Correct the phase delay, get the high frequencies out in front of the lower frequencies (in time) and you don't need as much gain to achieve improved detail.
However, if Max is going for the usual Analog good/Digital bad argument, he is barking up the wrong tree here. ONLY in the digital domain can you achieve linear phase equalization. In fact Linear phase digital EQ was a Holy Grail for a while (in the early 90's if I recall) until we learned that it didn't really sound any better than good old analog ringing-like-a-bell-all-the-non-linear-phase-delay-in-the-wo rld, equalizers. If the complaint is alluding to A to D converters, they are no longer at fault either, so I'm not sure where he is going with this. That is why I posted that I could be completely wrong in my earlier post, cause I don't know what is in his head with this issue. I think we would all like a bit of clarity from him.
Max, please pardon me for speaking about you in the third person.
Best Regards,
Bill
"Don't take it personally. But this shit is a science." J.J.Blair
“The Internet is only a means of communication,” he wrote. “It is not an amorphous extraterrestrial body with an entitlement to norms that run counter to the fundamental principles of human rights. There is nothing in the criminal or civil law which legalizes that which is otherwise illegal simply because the transaction takes place over the Internet.” Irish judge, Peter Charleton
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| Re: phase distortion [message #198069 is a reply to message #197584 ] |
Fri, 10 November 2006 16:41 |
maxdimario
Messages: 3811
Registered: December 2004 |
Platinum Member |
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my digital is bad, analog is good thing isn't at issue here.. what is at issue is phase distortion.
the fact that digital repro has strange phase anomalies in the top freq. range has nothing to do with me, or the things I say or do.. it is a fact as far as I know..
regardless.. this is a very serious issue for those who love music... if AUDIO is to be discussed..
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Re: phase distortion
