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Old 1st January 2013, 05:08 PM   #71
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Originally Posted by Pano View Post
I used Butterworth because that's what my editing software does. That's all I got.

Yeah, I could do the 2nd order vs 4th order/with phase correction. Want to pick a high pass frequency? Remember, it's supposed to be a box.
I would try at least a couple of different cutoff frequencies. Maybe 40Hz and 60Hz ? One to represent a larger speaker, the other for a bookshelf design.

Remembering of course that the cutoff of our own speakers / headphones we do the comparison on are going to impress their own rolloff on top of this...(hence not wanting to go too low with the first one causing the listening speakers/headphones to dominate the comparison)

You'd want a sample song that actually had some low bass in it too. Maybe it was my earphones but I didn't hear much in the way of low bass in your previous sample...
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Old 1st January 2013, 05:19 PM   #72
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Nevertheless it might be a good idea to test the audibility or threshold with decent headphones/earphones, and then do a separate test to see if there still is an audible difference with speakers.
Even with a STAX SR-202 I can't hear a difference.
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Old 1st January 2013, 05:51 PM   #73
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Which is what Andrew was getting at. Even good transducers and circuits aren't perfect in the bass. That's going to color what you hear in the test files.

I can try some other stuff, can anyone suggest a music sample to alter? The Steely Dan had pretty good energy below 100Hz, but not all the way down to 20. Not many do.
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Old 1st January 2013, 08:20 PM   #74
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Since you can't separate group delay from time shift (phase shift)(?), I'm not sure how valid a GD variation test can be. Phase shift or time shift will have consequences of their own. Left to right image location is very dependent on timing comparisons left to right and vice versa. Absolute (both channels in sync) time shift relative to the upper frequencies may or may not have perceptual consequences unless the delay is large (many periods).
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Old 1st January 2013, 08:40 PM   #75
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Originally Posted by Bob Richards View Post
Since you can't separate group delay from time shift (phase shift)(?),
Group delay is the first derivative of phase. In other words the magnitude of group delay at a given frequency is proportional to the slope of the phase at that frequency. Nothing more, nothing less.
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I'm not sure how valid a GD variation test can be. Phase shift or time shift will have consequences of their own.
How can it not be valid ? Add variation in the excess group delay (for example an all pass filter) and see if the effect is audible. That's the crux of the matter, is it audible or not, and what are the thresholds if it is...
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Left to right image location is very dependent on timing comparisons left to right and vice versa.
Indeed, however I think its implicit throughout all the discussion in this thread that any variations in group delay/phase etc are applied identically for left and right channels.
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Absolute (both channels in sync) time shift relative to the upper frequencies may or may not have perceptual consequences unless the delay is large (many periods).
Again, that's the crux of the issue. I would also like to draw a distinction between peaks in the excess group delay that typically occur at crossover frequencies, (due to the all pass nature of the summed crossover sections) and a shelf in the excess group delay caused by acoustic centre misalignment of drivers.

A group delay peak causes a slight delay in the propogation of the signal over a relatively narrow frequency range (more or less the crossover overlap region) while a shelf in the group delay (such as a tweeter too far forward) will cause a delay potentially over many octaves. (All the octaves below the crossover frequency in a 2 way with tweeter to far forward for example)

That may have a lower threshold of detection particularly in terms of effects on imaging. (Just speculating on this point)
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Old 1st January 2013, 08:57 PM   #76
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Originally Posted by Pano View Post
Which is what Andrew was getting at. Even good transducers and circuits aren't perfect in the bass. That's going to color what you hear in the test files.

I can try some other stuff, can anyone suggest a music sample to alter? The Steely Dan had pretty good energy below 100Hz, but not all the way down to 20. Not many do.
electronica for sure. Aphex twin? Orbital? Im fairly sure ive got something with with sub bass in it. I havent tried to use the testfiles, ive decided that i need a better soundcard since comparing an album in wav, and the same on CD.
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Old 1st January 2013, 09:20 PM   #77
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Try Yello's Touch album. Not sure it's 20Hz but is pretty low.
Other goodies - Lionell Rogg Toccata and Fuge - 1st track. Track 10 of the Drottningholm Baroque Ensemble (using St. Peters Stockholm, Church organ as bass - Before I got the tapped horns you don't really hear the deepest bass note.
These may be on Spotify.

I have had my Tapped horns (20-100Hz) both time aligned and not, and can't hear a difference to be honest. Using Holmimpulse square wave first positive, I measure that the tapped horns are ~5m behind the bass horn when not aligned.
DCX aligned the tapped horns perfectly with the bass horn- which is 100 - 330hz.
The bass horn and up are physically time aligned using Holmimpulse.
In my opinion time alignment is more critical the higher the freq - Necessary bass to mid horns. Absolutely essential on mid / upper horn and tweeter.


Quote:
Originally Posted by Pano View Post
Which is what Andrew was getting at. Even good transducers and circuits aren't perfect in the bass. That's going to color what you hear in the test files.

I can try some other stuff, can anyone suggest a music sample to alter? The Steely Dan had pretty good energy below 100Hz, but not all the way down to 20. Not many do.

Last edited by Speedysteve7; 1st January 2013 at 09:38 PM. Reason: corrected
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Old 1st January 2013, 09:23 PM   #78
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Back when I worked as an Engineering Assistant in baseband video engineering at Tektronix, some of the engineers there (super sharp guys) designed and built a doo-dad that would cause a significant anomoly in GD over a very limited frequency range, and there was a knob that would position it in frequency. They claimed that they could only hear it's effect in the upper midrange. I never got a chance to try it myself. I don't know anything else about the experiment.
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Old 1st January 2013, 09:27 PM   #79
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Originally Posted by DBMandrake View Post
How can it not be valid ? Add variation in the excess group delay (for example an all pass filter) and see if the effect is audible. That's the crux of the matter, is it audible or not, and what are the thresholds if it is...

Again, that's the crux of the issue. I would also like to draw a distinction between peaks in the excess group delay that typically occur at crossover frequencies, (due to the all pass nature of the summed crossover sections) and a shelf in the excess group delay caused by acoustic centre misalignment of drivers.
My intended point is that I don't know how you can introduce a significant GD anomaly without simultaneously creating a delay effect. How do you separate the two? How do you say the effect is from GD and not TD or phase shift?
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Old 1st January 2013, 09:34 PM   #80
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Here the are in reverse order

Drottningholm Baroque Ensemble / Vivaldi - Antonio Vivaldi: The Four Seasons, Op. 8

Bach / Lionel Rogg - Bach: Preludes, Toccatas and Fugues for Organ

Touch Yello CD Album
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