Phase shift audibility |
Post Reply | Page 123 8> |
Author | |
app
Old Croc Joined: 26 December 2013 Location: Finland Status: Offline Points: 2435 |
Post Options
Thanks(0)
Posted: 15 May 2015 at 12:23pm |
Yes or no?
I have my crossover before the mixer so I can get lo/mid/hi on separate channels in the mixer. Well yesterday I decided to test if it would make any difference to the sound is I change the phase of the mid and hi. And it surely did make a difference. It seems to me that there is much more detail in the sound and the whole sound got much better with this little "trick". What do you think,imagination or a fact? Related article! The audibility of absolute phase is nil. I must explain this further, as this is a somewhat contentious issue. It can be proven in ABX tests that there are some signals where the difference between a non-inverted and inverted signal is audible. Certain waveforms and instruments are highly asymmetrical, and if listened to in isolation will sound different if the phase is reversed. The difference is not subtle, either - it can be very pronounced. This is much more likely to be a result of loudspeaker driver behaviour than anything else, and the 'correct' phase is anyone's guess - should it be inverted or not? We don't know the answer, since we will be unsure of what the instrument sounded like 'live' - it is possible that neither the inverted or non-inverted recorded signal will sound like the original, so the point is moot. From Dr Floyd Toole: There have also been a great many tests, theories, arguments and counter-arguments about the audibility of phase shift. Many of the tests that have been done show that phase can be very audible, but usually only with contrived signals and test setups that are specifically designed to enhance audibility. From the number of websites and articles about phase audibility, it really looks like there are people desperately trying to prove that phase and/or phase shift is audible. So far, none has succeeded - the basic assumption that we are not sensitive to phase (with real-life signals at least) holds true. If we listen to a saxophone (a good example of an asymmetrical waveform) with the phase normal then reversed, all we hear is a difference - there is not necessarily a 'right' or 'wrong' phase, since it depends on the way the instrument was miked in the first place. If the period between listenings is extended to a few minutes, the chance of us hearing the difference will be minimal, and we still won't know which is 'right' and which is 'wrong' - all that this proves is that there is a difference, and it only becomes audible with some instruments. This is probably the only case where an ABX test proves something that is not relevant in the general sense - so yes, absolute phase can be audible, but it is (generally) irrelevant. While it may be possible to pick a difference, it is only a difference - neither sounds 'better' than the other. The net result is that our ears do not care if there is a slight misalignment between the fundamental and harmonics of any instrument known. This is likely to cause howls of protest from people who won't actually bother to read this article in its entirety (if at all), but it has been demonstrated time and time again, and by various techniques. http://sound.westhost.com/ptd.htm |
|
"what!?"
|
|
Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7216 |
Post Options
Thanks(0)
|
Yes, it most probably doesn´t make much difference if you´re listening to horribly compressed mp3.
|
|
Earplugs Are For Wimps!
|
|
audiomik
Old Croc Joined: 06 April 2010 Location: Bath, UK Status: Offline Points: 2962 |
Post Options
Thanks(0)
|
To properly reproduce a sound source, the signal path and 'Speakers should have a zero phase response for it's entire frequency bandwidth.
Otherwise you are not hearing through the system the original sound from the source! Mik Edited by audiomik - 15 May 2015 at 1:50pm |
|
Warning! May contain Nuts
plus springs, washers, screws, etc, etc. |
|
odc04r
Old Croc Joined: 12 July 2006 Location: Sarfampton Status: Offline Points: 5482 |
Post Options
Thanks(0)
|
The effect of phase shifting adjacent frequency bands is not one that is hard to figure out the effect of. Of course it will change the sound.
|
|
snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3121 |
Post Options
Thanks(0)
|
but the phase relationships of the original source material were entirely arbitrary to start with. if you record an instrument at 1m or at 2m you will get a different recording. you could perfectly reproduce the recording but the phase relationships will only hold for one listening position.
the OP has probably just boosted the response in the crossover region ~2kHz
|
|
Xoc1
Registered User Joined: 15 October 2012 Location: Devon UK Status: Offline Points: 397 |
Post Options
Thanks(0)
|
The crossover will cause phase shifts at the crossover points. The amount of phase shift will depend on the filter order used in the crossover. So how the split frequency bands combine in the mixer will depend on the filter used.
If you used a 12db second order filter you would need to reverse the mid band to get everything to line up. If you used a 24db fourth order then you should not need to reverse any phases. |
|
pfly
Old Croc Joined: 25 October 2007 Location: Helsinki, Fin Status: Offline Points: 2828 |
Post Options
Thanks(0)
|
His crossover is most likely 24dB unit.
Flipping the polarity (this is not same as phase exactly) on mid and hi will not change the way you are hearing those two. However, by polarity reversal on those two bands, the summation of low and mid bands will be compromised when you are summing those two bands back together. Ruler flat phase response throughout the system would mean that system's time behaviour would be optimum. Hearing an altered phase shift is different thing. At least in these kind of cases phase is relative, with single signal some phase change does not change the way human hears the sound. When summing two copies of same signal, then it's different thing. |
|
audiomik
Old Croc Joined: 06 April 2010 Location: Bath, UK Status: Offline Points: 2962 |
Post Options
Thanks(0)
|
Seems that our often forgotten enemy TID has been missed out!
Mik Edited by audiomik - 16 May 2015 at 9:13am |
|
Warning! May contain Nuts
plus springs, washers, screws, etc, etc. |
|
Darkstar
Registered User Joined: 08 October 2014 Location: Italy Status: Offline Points: 326 |
Post Options
Thanks(0)
|
Phase shifts can cause cancellations in the frequency spectrum right where each different component is filtered at: eg. LPF sub to HPF mid
Remember that if you sum two identical sound waves with exact opposite phase they generate silence. Rooms also affect this, I remember having to phase invert subs in a pub once otherwise bass would be inaudible (I was using full range tops). Same exact system in other places didn't need phase inversion. Edited by Darkstar - 16 May 2015 at 11:08am |
|
Bass =/= Enough
|
|
IanD
Registered User Joined: 17 January 2009 Location: London Status: Offline Points: 400 |
Post Options
Thanks(0)
|
Phase shifts between different sources (crossovers, drivers) are audible because they cause peaks or (more often) dips in the frequency response.
The quoted post was saying that phase shifts or inversions in one signal -- which don't cause any changes in amplitude response -- are somewhere between barely audible (under some conditions) and inaudible (under most conditions). I had exactly the same discussion about phase shifts at university in the late 70's when phase alignment was a hot topic and many people insisted it was audible because that's what many of the hi-fi mags were saying. So I built a high-quality sweepable all-pass filter/inverter, inserted it in the signal path in my (good quality) hi-fi, and invited the phase-a-holics round to listen. Regardless of source material (vinyl, decent turntable/cartridge -- this was before CDs and MP3s), speaker or headphones, nobody could spot either an inversion or a phase shift (allpass filter). Anyone who disagrees, try the same experiment yourself (but with somebody else doing the ABX selection so you don't know what you're listening to). But be warned, like the cable-a-holics, nobody else has been able to reliably tell the difference either :-) Edited by IanD - 16 May 2015 at 1:04pm |
|
audiomik
Old Croc Joined: 06 April 2010 Location: Bath, UK Status: Offline Points: 2962 |
Post Options
Thanks(0)
|
try your filter method with percussion only!
Also try using multi frequency (harmonically related) impulse responses. Mik |
|
Warning! May contain Nuts
plus springs, washers, screws, etc, etc. |
|
IanD
Registered User Joined: 17 January 2009 Location: London Status: Offline Points: 400 |
Post Options
Thanks(0)
|
As the quote said, if you select especially sensitive test cases under ideal conditions it *may* be possible to tell the difference. But unless your idea of a good time is sitting in an anechoic chamber listening to solo snare drum, this isn't really relevant. Listening to music -- even testing material with a lot of percussion -- nobody could spot the difference when I tried it, and this agrees with all the other findings I've seen. So I guess the burden of proof is on anyone who thinks signal phase shift/polarity is important when listening to music, not artificial test signals... ;-) P.S. TID is just another word for distortion under high slew-rate conditions, any competent circuit designer should be able to prevent this happening :-) Edited by IanD - 16 May 2015 at 1:56pm |
|
Post Reply | Page 123 8> |
Tweet |
Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |