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-   -   "The phase coherence of harmonics in the vocal formant range, ~630Hz to 4000Hz" (http://www.diyaudio.com/forums/multi-way/223714-phase-coherence-harmonics-vocal-formant-range-630hz-4000hz.html)

Elias 16th November 2012 09:17 PM

"The phase coherence of harmonics in the vocal formant range, ~630Hz to 4000Hz"
 
The thread title is one of the key points from David Griesinger's presentation:
"Pitch, Timbre, Source Separation"
http://www.davidgriesinger.com/Acous...b_sound_3.pptx


Looks like he has come to a conclusion many fundamental auditory perceptions are derived from the property:
"the phase coherence of harmonics in the vocal formant range, ~630Hz to 4000Hz"



Now, this can have some interesting consequencies to the sound reproduction over loudspeakers in a small room, too.

In order to achieve the above requirement we would need at least:

* phase linear loudspeaker over this freq range

* No cross over within this freq range

* No cabinet difractions within this freq range

* No early room reflections in this freq range

* Modulation transfer function of unity in this freq range



It's all nice, BUT, what will happen to the harmonic phase coherence when you put 2 loudspeakers in a triangle and get terrible stereophonic comb filtering at the listening position ? :rolleyes:

There should be at least one possible solution to reproduce sound over loudspeakers while the above requirements remain achievable: Cross talk cancelling ;)



- Elias

Barleywater 16th November 2012 09:30 PM

The properties of stereo phantom image formation remains highly intact for speaker pairs that mash up phase in similar fashion.

When signal content in one speaker undergoes different mashing, such as with driver break up modes, or poorly behaved passive crossover, phantom image is degraded.

Asymmetrical lateral early reflections distort imaging. And identity of source as some manner of speaker due to speaker transfer function is nothing new.

Take home message of David Griesinger is that virtually all sources with low frequency components have harmonic content which is faster for brain to decode into locational cues.

Regards,

Andrew

Rudolf 16th November 2012 10:21 PM

Elias,
as I understand Griesinger, the phase coherence is not a value in itself, but is helping the brain to decipher the individual(s) formants in each critical band filter. I'm referring to foil 28 here. So the phase coherence must be sufficient in each critical band (and some region left and right of it perhaps), but not linear for the complete vocal formant range.
Room reflections certainly are an issue. Cabinet diffractions can be an issue if not dealt with in the way I do ;) :D.

Rudolf

jcx 16th November 2012 10:25 PM

yes matching phase response is all that is required to maintain "phase coherence" between channels

but it is reported to be possible to train to decern large mid frequency crossover phase shift - but as far as I know independent of "imaging"

mondogenerator 16th November 2012 11:08 PM

Elias: I think that most of your ideals could be achieved.

#1: agree, but isnt that impossible?
#2: agree. Quite possible.
#3: again I agree, and its quite possible to achieve.
#4: the band of freqencies you quote would suit judicious room treatment.
#5: i use transfer functions but never the modal variety ;) Would getting #2, 3 and 4 be close enough to achieving #5?

Barleywater 16th November 2012 11:39 PM

#1 has already been achieved:

http://www.diyaudio.com/forums/attac...e-overlays.png

#2 is not a requirement;

#3 is effectively achieved by speaker system to demonstrate #1

#4 follows from #3 and good speaker placement

#5 for described speaker is exceptional

DSP based Pluto Clone has amazing imaging.

Regards

Andrew

dewardh 16th November 2012 11:52 PM

Quote:

Originally Posted by Barleywater (Post 3244501)
DSP based Pluto Clone has amazing imaging.

Even "analog" PLUTO is none to shabby in that regard . . .

It's not even a new argument . . . "300-3000" has been described as a "critical range" for a long time. 700-4000 should be easier to achieve with a single driver . . (hmmm . . . PLUTO almost does . . .)

Elias 17th November 2012 08:54 AM

Quote:

Originally Posted by Rudolf (Post 3244430)
Elias,
as I understand Griesinger, the phase coherence is not a value in itself, but is helping the brain to decipher the individual(s) formants in each critical band filter. I'm referring to foil 28 here. So the phase coherence must be sufficient in each critical band (and some region left and right of it perhaps), but not linear for the complete vocal formant range.

Interesting argument, but as single critical bandwidth does not yet fully determine the timbe nor pitch the comparison is made through the full freq range. And, taking into account the critical bandwidth is not a discrete value consept but a smooth continous filtering phenomena then it follows that as phase linearity is required within one band it is required along the whole freq band.

As noted in other posts linear phase is approachable with engineering.


Quote:

Originally Posted by Rudolf (Post 3244430)
Room reflections certainly are an issue. Cabinet diffractions can be an issue if not dealt with in the way I do ;) :D.

Rudolf

Also maybe a big non diffracting horn like JMLC would do.


- Elias

Elias 17th November 2012 08:56 AM

Quote:

Originally Posted by jcx (Post 3244437)
yes matching phase response is all that is required to maintain "phase coherence" between channels

but it is reported to be possible to train to decern large mid frequency crossover phase shift - but as far as I know independent of "imaging"

The issue was not a coherence difference but the absolute value.

Elias 17th November 2012 08:58 AM

Quote:

Originally Posted by mondogenerator (Post 3244472)
Would getting #2, 3 and 4 be close enough to achieving #5?

Could be enough. The MTF could serve as a metric.


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