CHANGSTAR: Audiophile Headphone Reviews and Early 90s Style BBS

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Author Topic: Convolve CSD plots with minimum phase FIR filter?  (Read 9117 times)

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Solderdude

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Re: Convolve CSD plots with minimum phase FIR filter?
« Reply #50 on: October 15, 2012, 04:59:38 AM »
Subtle indeed  :D

At least not consistent with the waterfall plot as the ringing doesn't appear to have gone as in the plot, it seems to be just altered in a tiny way.
I assume the scale is linear in amplitude.
The waterfall plot still baffles me as it implied ringing is gone completely and complete FR is as flat as a pancake.
I would expect (but may assume falsly) that when one lowers the amplitude so it is flat say by 10dB or so the ringing would stop earlier but still be there.

Have to look which thread it came from and what the rest of the findings were. :)p8
Maybe there is a hint about how it sounded as well.
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ultrabike

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Re: Convolve CSD plots with minimum phase FIR filter?
« Reply #51 on: October 15, 2012, 06:41:35 AM »
LOL! I didn't show an equalized IR. I was just discussing some minimum phase stuff.

Here are some quick and dirty FIR convolution equalizer results (150 tap pseudo-optimized using LMS) just as a proof of concept.

1) I used Tyll's IR which lacks information < 200Hz so not ideal.
2) The filter is pure FIR. I could have done a pole cancellation deal (like xnor.) However, if zeros move a bit (as in positional variation) I have a feeling this may not work very well.
3) I didn't optimize this at all, I really just gave it a whirl.

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Solderdude

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Re: Convolve CSD plots with minimum phase FIR filter?
« Reply #52 on: October 15, 2012, 11:10:41 AM »
Ah... that's more like it.

It seems the 'sibilance' and 'over detailing' of the K701 should have been improved in more than a subtle way !
HOW did it sound ?
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ultrabike

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Re: Convolve CSD plots with minimum phase FIR filter?
« Reply #53 on: October 15, 2012, 04:35:59 PM »
Thanks Solder. Unfortunately, I don't know how it would sound... yet. Would need a DSP in the chain (for the FIR) and the actual headphones (perhaps a measurement rig as well.) Maybe one day :)p5

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Joe Bloggs

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Re: Convolve CSD plots with minimum phase FIR filter?
« Reply #54 on: October 15, 2012, 05:26:24 PM »
Quote from: Solderdude on October 15, 2012, 11:10:41 AM
Ah... that's more like it.

It seems the 'sibilance' and 'over detailing' of the K701 should have been improved in more than a subtle way !
HOW did it sound ?

Prolly no good at all as flat FR sounds no good coming from headphones unless it's a binaural recording...  :)p2
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ultrabike

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Re: Convolve CSD plots with minimum phase FIR filter?
« Reply #55 on: October 15, 2012, 05:42:38 PM »
No worries, one can equalize to whatever target (not just flat)...
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arnaud

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Re: Convolve CSD plots with minimum phase FIR filter?
« Reply #56 on: October 15, 2012, 08:44:38 PM »
Yep .... Got to get my act together on this one, less talk more action ;)
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Solderdude

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Re: Convolve CSD plots with minimum phase FIR filter?
« Reply #57 on: October 16, 2012, 04:58:26 AM »
Analog filters I can do, digital I have no idea how.
If PCB's need to be designed I can be of assistance.

For the practical side of things one would need a 'service' where to send the headphones to and have it measured and a 'counter' EQ made and poored into a DSP.
Also that DSP would have to have the possiblity to add a little bass and or tilt the response by the end user to match the individuals taste.
Or they would be selling 'corrected' headphones with said device.
Arduino boards may be suited.

A flat headphone sounds good to me at higher SPL, to be listening at say 70 to 80dB SPL a little lift in the lows is really appreciated.
Fletcher and Munson already determined that as well almost 100 years ago.
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Joe Bloggs

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Re: Convolve CSD plots with minimum phase FIR filter?
« Reply #58 on: October 16, 2012, 08:50:04 AM »
Flat headphone FR sounds bad because of the difference between loudspeaker and headphone HRTF, not because of Fletcher-Munson curves...
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Solderdude

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Re: Convolve CSD plots with minimum phase FIR filter?
« Reply #59 on: October 16, 2012, 07:33:08 PM »
To my ears flat speakers and flat (measuring without any HRTF applied) headphones (equalized or not) sound very 'real' at higher SPL's.
At low SPL's both do sound 'boring' and un-engaging.
I guess the last part is what you mean with 'bad sounding'.
It just doesn't appear to me that way (as bad sounding)...
I even prefer it that way, though some nicely 'colored' headphones may sound more yummy on certain recordings.

HRTF is nothing more than a fixed amount of 'correction' used on the raw data (meaning the sounds the mic detected) and the result is supposed to be an 'approximation' of what many people would feel it would sound like.
HRTF is not an SPL related correction factor and therefore doesn't account for the perceived loss of bass at lower SPL, making them sound boring and lifeless on lower SPL.
FM curves do, that's why I mentioned them.
There are different HRTF and some HP sites use different HRTF because it 'fits' their ideologies better or more closely matches their 'ears/brain' and also for different 'fields' of correction.
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