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Author Topic: delay estimation and measurement  (Read 15520 times)

Raimonds.Skuruls

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delay estimation and measurement
« on: February 12, 2014, 06:04:29 am »

Everyone knows how delay estimation is challenging.
What about such kind of view on delays of 4 band loudspeaker system?

We can see that driver band is delayed about 1 ms after tweeter.
Midwoofer is delayed about 0.7 ms after tweeter.
If time span of graph is changed to 20 ms, we can see that LF band is delayed for about 8.3 ms.

And same graphs in isometrics.

It is possible to create Delay Frequency Response from such graph.

You can find few more examples here
http://aplaudio.com/downloads/Introduction-to-TDA.pdf
Can this be helpful for your system tuning and commissioning everyday job?

BR,

Raimonds Skuruls
http://aplaudio.com

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Tim McCulloch

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Re: delay estimation and measurement
« Reply #1 on: February 12, 2014, 10:33:33 am »

Looks like a "pretty picture" way of doing an impulse alignment.  Ivan? Chris? Timo? Langston?
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Timo Beckman

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Re: delay estimation and measurement
« Reply #2 on: February 12, 2014, 02:41:09 pm »

I've seen this kind of a plot before and it's a nice picture but to me (underscore please) that's all it is.

I can do a lot more working with a phase display (or it's derivative group delay although the last time i looked at that is about a year ago after a "pissing contest" on a dutch forum).

Impuls alignment is something i do not use on system aligning a 2/3/4 or more way system. Has to do with High-pass and Low-pass filters causing group delay and thus changing "time" and the ir.
@ the topic starter you want to see something like the screen shots in this post at my blog.
http://timobeckmangeluid.wordpress.com/2013/01/12/again-playing-with-phase/
Here you find screenshots of the phase display and it's derivative the group delay screen which is what you're asking in my opinion?
 
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Chris Tsanjoures

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Re: delay estimation and measurement
« Reply #3 on: February 12, 2014, 03:31:16 pm »

I would agree with Timo, the phase plot is the preferred view for time measurements. I can imagine the 3d spectrograph being useful for things like analyzing decay times, however rendering the 'slices' on the frequency scale rather than time is a red flag for me.
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Ivan Beaver

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Re: delay estimation and measurement
« Reply #4 on: February 12, 2014, 06:53:07 pm »

I am not understanding this question

"It is possible to create Delay Frequency Response from such graph."

If the question is can you show the freq response from such a graph-I highly doubt it-mainly because there is not out of band information.

So I doubt it would be much good in trying to do a system alignment.

A simple phase repsonse is easier to read and show the interaction between different freq bands.

This seems to "stop" at the edges with no overlap
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Arthur Skudra

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Re: delay estimation and measurement
« Reply #5 on: February 12, 2014, 08:25:45 pm »

Sveiki Raimonds!

Interesting software you have there!  I certainly like the 3D view, helps visualize certain characteristics of the loudspeaker.  Not sure if it's application in live sound reinforcement is useful for us in live concert sound, especially when room acoustics has considerable influence on what we see with our measurements, and in some ways makes it challenging to interpret the data displayed on the computer.

In measuring large scale sound reinforcement systems in very large rooms, most of us audio practioners use the impulse response for finding the general delay of a loudspeaker to get the dual channel FFT to be properly synchronized, then either use the phase plot or the group delay to figure out where in time certain frequencies arrive.

Though for some beginners it's hard to grasp the concept of phase at first, when it becomes clearer it is a very powerful tool for sound system alignment.

Arthur Skudra
« Last Edit: February 12, 2014, 08:33:30 pm by Arthur Skudra »
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Raimonds.Skuruls

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Re: delay estimation and measurement
« Reply #6 on: February 13, 2014, 09:46:56 am »

Yes, we can try to catch parallel phase responses by switching on and off some bands, but,
as you are not so close to a loudspeaker, as you are going down on frequency scale, as you have particular loudspeaker resonances, it is more and more difficult to realize that basic approach.
That’s because we need to get the reliable phase response. We can get it from impulse response by use of FFT. But impulse response (in real acoustic environment) is very noisy because of random reflections of environment. It means, the phase response is also heavy disturbed, noisy. Only serious smoothing helps little bit, but by the price of loosing valuable information. And if we are trying to calculate group delay from such phase response, we are going into deeper errors because of calculation of a derivative of the phase response.
This insoluble problem stirs me to action. Especially in car audio field, where problem of delay evaluation is very serious. (By the way, the car equipped with 6 channels of APL correction, performed the best sound in European final of EMMA car sound competition...)

I have processed lot of my previous medium and large scale (concert) loudspeaker system (including serious brands) measurements and did not find even one that was correctly tuned.
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Timo Beckman

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Re: delay estimation and measurement
« Reply #7 on: February 14, 2014, 04:36:58 am »

So what would a correctly tuned set-up look like to you on a analyzer if i may ask?
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Raimonds.Skuruls

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Re: delay estimation and measurement
« Reply #8 on: February 14, 2014, 05:28:16 am »

So what would a correctly tuned set-up look like to you on a analyzer if i may ask?
Thank you for a question!
If we have an ordinary IIR crossover, we must see just delays introduced by a crossover unit.
Picture  „crossover4way4order.png” is showing  delays of 4 way 4 order crossover.

If we have linear phase crossover we must see ideal transfer.
Picture „1.png”.

Real speaker must looks like this (2 way, 2 order crossover, no place to make delay mistake).
Picture „1_NS10.png” - NS10 monitor.

But we can improve it by minimum phase correction of Amplitude Frequency Response.
Picture „2_NS10_APL_mp_AFRcor.png”

And than, by introducing time correction – picture „3_NS10_APL_mp_AFRcor_TIMEcor.png”


« Last Edit: February 14, 2014, 08:46:56 am by Raimonds.Skuruls »
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