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Author Topic: TDA – Time Domain Analysis software  (Read 1670 times)

Peter Morris

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TDA – Time Domain Analysis software
« on: June 19, 2014, 09:15:59 am »

I have down loaded and had a play Acoustics Power Labs TDA demo software.

First impressions; it looks fantastic!

I tried it to optimising some of my DSP speaker’s settings shown below. Unfortunately I didn't keep a copy of the initial plots to show what can be done.  Please note that the acoustic environment was not very good and the LF was a reflex 21”.

The plots are of our own 2 x 10” + horn and a Flex array with my DSP settings (Lake LM26).

On the bottom plot you can see a little bit of diaphragm breakup around 17 kHz. The box uses an eighteen sound NDS1480N compression driver with a nitride coated diaphragm, and as noted by eighteen sound's product information, this is where it will occur. http://www.eighteensound.com/PRODUCTS/Products/ProdID/151/CatID/28#.U6LneWkiPq4

Looking forward to reading the road-test.
http://www.prosoundweb.com/article/road_test_coming_up_tda_--_the_worlds_first_delay_analysis_software/

Anybody else tried it?

Peter
« Last Edit: June 20, 2014, 01:49:20 am by Peter Morris »
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Frank Koenig

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Re: TDA – Time Domain Analysis software
« Reply #1 on: June 20, 2014, 02:51:41 pm »

This is a subject of some interest to me and, for what it's worth, I slogged through Skuruls's patent (US8121302B2, Feb. 2012) to try to see what's there. (It's tough going with the poor English translation and absence of common signal-processing terminology.)

Part of it appears to be concerned with capturing the system function at multiple points in a reverberant environment. Other than choosing an advantageous spatial sampling of the acoustic space I couldn't really make head nor tails of it. He refers to an "inverse spectrum function", which is used to filter the impulse responses, but I don't see where it comes from. In any case, this business of trying to back-out the room is not very interesting to me since, like most of us, I choose a measurement environment free of reflecting surfaces within range of the part of the impulse response interest.

The rest of the patent is concerned with generating an FIR filter from the multiple impulse responses (IRs). So near as I can tell these are the steps:

Align the IRs at their peaks.

Average the IRs.
 
Window the average.

Take the DFT (which he keeps referring to as "the FFT").

Apply constant octave-bandwidth smoothing to the magnitude of the frequency response (which I assume is what he means by the "acoustic power frequency") by convolving with a log-scaled raised cosine.

Fix up the ends of the magnitude to provide the "don't care" for the inverse filter.

Separately smooth the unwrapped phase by smoothing the group delay by unspecified means.

Put the mag and phase back together and invert to create a prototype correction filter.

Generate FIR coefficients from the prototype by unspecified means but I assume he uses an IDFT and window.

I don't see any attempt to separately correct the minimum and non minimum phase parts nor any sophistication with respect to how the IRs are combined. Or course, the software may do things that are not in the patent.

The breathlessness of the Web site and the Pro Sound Web article are a bit off-putting, too, but if it works, who cares? What do you all think?

--Frank
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Peter Morris

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Re: TDA – Time Domain Analysis software
« Reply #2 on: June 21, 2014, 10:11:16 pm »

Hi Frank,

As you are aware, there are two parts to what he is doing – the TDA measurement software and the APL1 FIR box.

There is also APL Workshop software which will create the FIR tap coefficients and transfer them to the APL1 to create a flat frequency, phase and power(?) response.  I don’t know how it deals with things that are not minimum phase but he does talk about in some of his posts.

I did something like this manually using Smaart and the Lake controller to get the best result in the room I could.  https://www.youtube.com/watch?v=-LLYkGj7Zbk

Then I used the Demo software, manually adjusting the frequency response on a Lake LM26 after looking at the acoustic power frequency response graph TDA produced, and time/frequency/amplitude graphs I posted above.

The question I had was; did this result in something that sounded better in a room than just using Smaart. Yes I think so … but that’s just one quick poorly defined experiment/test. 

Edit ... tried a few more tests and it seems to work.  It provided a more balanced sound to my ear than I could get with smart or systune. I assume that's because it included those bit of the reverberant sound field that our ears take notice of in the acoustic power frequency response plot.
« Last Edit: June 23, 2014, 10:17:59 pm by Peter Morris »
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Peter Morris

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Re: TDA – Time Domain Analysis software
« Reply #3 on: June 25, 2014, 09:17:47 am »

Hi Frank,

As you are aware, there are two parts to what he is doing – the TDA measurement software and the APL1 FIR box.

There is also APL Workshop software which will create the FIR tap coefficients and transfer them to the APL1 to create a flat frequency, phase and power(?) response.  I don’t know how it deals with things that are not minimum phase but he does talk about in some of his posts.

I did something like this manually using Smaart and the Lake controller to get the best result in the room I could.  https://www.youtube.com/watch?v=-LLYkGj7Zbk

Then I used the Demo software, manually adjusting the frequency response on a Lake LM26 after looking at the acoustic power frequency response graph TDA produced, and time/frequency/amplitude graphs I posted above.

The question I had was; did this result in something that sounded better in a room than just using Smaart. Yes I think so … but that’s just one quick poorly defined experiment/test. 

Edit ... tried a few more tests and it seems to work.  It provided a more balanced sound to my ear than I could get with smart or systune. I assume that's because it included those bit of the reverberant sound field that our ears take notice of in the acoustic power frequency response plot.

Had a little more time to play with the program - the results are stunning, producing a flat power response sounds better than producing a flat SPL.  I initially used Systune to create the DSP settings and then fine tuned the power response with TDA. I was able to get the system to reproduce my voice so accurately that it didn't sound like a PA ... it was like I was just standing some else.

Here are a couple of before and after plots. FWIW the crossover points are 125Hz and 900Hz.
« Last Edit: June 25, 2014, 09:25:42 am by Peter Morris »
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Raimonds.Skuruls

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Re: TDA – Time Domain Analysis software
« Reply #4 on: June 26, 2014, 06:41:23 am »

Thanks, Peter, for the experiment.
If an equalization (minimum phase) of AFR is applied in a right place on frequency scale and in a right amount, you will have improvement in Phase Frequency Response also and will see it on TDA graphs like you already have. Thanks for your results!
If you are using linear phase equalizer you will not get such results.
You can find more about this here on example of Quested monitors:
http://forums.prosoundweb.com/index.php?topic=148306.msg1368687#msg1368687

This is a subject of some interest to me and, for what it's worth, I slogged through Skuruls's patent (US8121302B2, Feb. 2012) to try to see what's there. (It's tough going with the poor English translation and absence of common signal-processing terminology.) ......
Thank you for reading a description of the my previous work, already 10 years old.
You are wrong with assumption that TDA is based on that work and that TDA is using multiply IRs.
TDA is using just one IR. There is just a one similar thing with previous work – using of a sweep test signal. Nothing more.
Please, take demo from APL web site, to avoid such kind of misunderstanding.

I assume that you have true passion about sound reproduction things as you are here and writing here.
If so, you must be familiar with developments and products, offered 8 years ago in at least 3 AES conventions, not just in theory. You must be familiar with products that implement this 10 years old solution.

US8121302B2 is a patent not just an application. You are little bit late with opinion that it is not completely described or do not have innovative step.
Some company, that is offering “ordinary RTA”, is expressing in its update history that they:
“Changed default live average and trace average for spectrum traces to Power instead of dB averaging.” It is core of US8121302B2 but they implementation is very ineffective.
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Peter Morris

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Re: TDA – Time Domain Analysis software
« Reply #5 on: June 28, 2014, 12:24:51 am »

Hi Raimonds,

My experience and impression so far is the same as John’s in the link you posted.  It’s like you are in the studio listening to the band live, not the monitors! As john noted, the reverb detail is extraordinary.
« Last Edit: June 28, 2014, 11:54:09 am by Peter Morris »
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Jason Joseph

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Re: TDA – Time Domain Analysis software
« Reply #6 on: June 30, 2014, 10:19:25 am »

Hi Raimonds,

My experience and impression so far is the same as John’s in the link you posted.  It’s like you are in the studio listening to the band live, not the monitors! As john noted, the reverb detail is extraordinary.

Peter would you care to share some insight on the hardware you used? Just want to get the complete picture as I delve into the unknown of testing and analysis... Thanks in advance..
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Frank Koenig

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Re: TDA – Time Domain Analysis software
« Reply #7 on: June 30, 2014, 01:08:56 pm »

For anyone late to the party, like me, here's a link to a most interesting thread from ~2008.

http://forums.prosoundweb.com/index.php?topic=97505.0

--Frank
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Peter Morris

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Re: TDA – Time Domain Analysis software
« Reply #8 on: June 30, 2014, 08:15:18 pm »

Peter would you care to share some insight on the hardware you used? Just want to get the complete picture as I delve into the unknown of testing and analysis... Thanks in advance..

Hi Jason,

Hardware – i5 Lenovo laptop, small mixer with phantom power, & an Earthworks M30 mic. There can be a few tricks getting the sound card to work as you need – stereo line in and stereo out.

I also have a "pink stick" or phantom powered pink noise gererator that Rational Acoustics sell. They also have a nice mic pre but its a bit expensive ...

I use Systune and its internal pink noise source to do the initial EQ and crossover design and then TDA to correct the power response.  TDA uses a sine wave sweep generator that is part of the software.
« Last Edit: June 30, 2014, 08:19:06 pm by Peter Morris »
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David Sturzenbecher

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Re: TDA – Time Domain Analysis software
« Reply #9 on: June 30, 2014, 08:50:01 pm »

For anyone late to the party, like me, here's a link to a most interesting thread from ~2008.

http://forums.prosoundweb.com/index.php?topic=97505.0

--Frank

So, does anyone know if Bennett ever followed up?
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