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Author Topic: APL's Time Domain Analysis - Update?  (Read 2380 times)

Lee Richard

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APL's Time Domain Analysis - Update?
« on: August 09, 2015, 03:50:49 am »

Last June PSW posted an "upcoming road test" article about Raimonds Skuruls's TDA software, and how it was being tested in the US. Has anything come from that? They never posted the actual road test, so I was wondering if anyone else has been using it. APL Audio now has a half rack hardware box to apply the TDA settings with Analog and AES/EBU i/o. Has anyone tried it?

-Lee

Doug Fowler

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Re: APL's Time Domain Analysis - Update?
« Reply #1 on: August 09, 2015, 01:07:41 pm »

Last June PSW posted an "upcoming road test" article about Raimonds Skuruls's TDA software, and how it was being tested in the US. Has anything come from that? They never posted the actual road test, so I was wondering if anyone else has been using it. APL Audio now has a half rack hardware box to apply the TDA settings with Analog and AES/EBU i/o. Has anyone tried it?

-Lee

I have the software and will produce the review next week for the magazine.  Stand by...
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Merlijn van Veen

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Re: APL's Time Domain Analysis - Update?
« Reply #2 on: August 09, 2015, 03:24:42 pm »

Woohoo!


Verzonden vanaf mijn iPad met Tapatalk
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Peter Morris

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Re: APL's Time Domain Analysis - Update?
« Reply #3 on: August 09, 2015, 07:55:45 pm »

Last June PSW posted an "upcoming road test" article about Raimonds Skuruls's TDA software, and how it was being tested in the US. Has anything come from that? They never posted the actual road test, so I was wondering if anyone else has been using it. APL Audio now has a half rack hardware box to apply the TDA settings with Analog and AES/EBU i/o. Has anyone tried it?

-Lee

I have the TDA software and the ALP1 … they’re great.
 
I have used TDA to help me EQ a system for musical production - probably the best results I have ever had.

I also used it in designing this project – https://soundforums.net/threads/11317-New-DIY-Mid-High/page16 see post 74
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Doug Fowler

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Re: APL's Time Domain Analysis - Update?
« Reply #4 on: August 13, 2015, 12:05:12 pm »

I have the TDA software and the ALP1 … they’re great.
 
I have used TDA to help me EQ a system for musical production - probably the best results I have ever had.

I also used it in designing this project – https://soundforums.net/threads/11317-New-DIY-Mid-High/page16 see post 74

Peter, pls. check your PMs.

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Jack Arnott

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Re: APL's Time Domain Analysis - Update?
« Reply #5 on: February 10, 2016, 05:37:32 pm »

I have the software and will produce the review next week for the magazine.  Stand by...

I just looked in Audio Measurement and Testing, and Road Test, and do not see any reports. Is this still in the works?
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Merlijn van Veen

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Re: APL's Time Domain Analysis - Update?
« Reply #6 on: February 12, 2016, 06:41:30 am »

Yes. How's that coming. Lots of interest.
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Jack Regula

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Re: APL's Time Domain Analysis - Update?
« Reply #7 on: February 18, 2017, 11:42:41 am »

Yes. How's that coming. Lots of interest.
One year or so later, is this still a hot topic?   I'm a DIYer and have been using TDA for about 6 months and I like to write so let me jump in. 

TDA, from Acoustics Power Labs, provides a new way of looking at the responses of speakers in rooms.  Its Intuitive 3D Display of sound level vs arrival time and frequency spotlights speaker and room anomalies. 

An impulse response shows energy arrival over time; TDA shows both the amplitude and the spectrum of that arriving energy over time.  It is useful in both the design and fine tuning of the speakers themselves, especially their crossovers, and in integrating those speakers into rooms.  TDA is the analysis step on a ladder of tools from APL that provide increasingly more powerful equalization solutions for adapting speakers to listening spaces.
TDA uses a sine sweep to obtain an impulse response that can be viewed by use of the IR and Log IR buttons on its control panel.  The calculated impulse response contains non-linear distortion information that can also be displayed.  Distortion can also be seen as a series of spikes before the main peak of the IR in the log IR view.  Third party tool IRs can also be imported and viewed.

The obtained IR is then processed by TDA at 126 frequencies, 12 log spaced points per octave to create its unique 3D display - a 3-dimensional map of normalized sound pressure plotted with delay and frequency along the X and Y axes and SPL encoded in both color and on the Z axis.   Boundary effects, room modes, timing alignment issues with multi-way speakers, and frequency response aberrations are easily recognized in this presentation. This 3D map is a very good tool for quickly evaluating a new speaker in a familiar space or a familiar speaker in a new room or position.

TDA also provides conventional frequency, delay, and phase response graphs.  TDA attempts to separate the direct response from reflections based on time of arrival and succeeds in doing so down into the modal zone to an extent limited by room modes, near reflections and the increased difficulty of precisely determining the time of arrival of low frequencies. This time selectivity enables us to see both the direct response, otherwise viewable only as an anechoic or quasi-anechoic measurement, and the effect of the room. It’s not a coincidence that the human ear has the same/similar ability to separate direct sound from reflections and the same/similar limitations. 

TDA’s frequency response graph, the AFR, shows this separated direct response while its 3D display allows you to judge the extent to which it stands above room and boundary effects.  Where it is reflection free, it is minimum phase and thus can guide equalization; other products from APL use multiple AFRs taken at multiple positions to do just that.

The review will continue in additional posts.  Meanwhile, you can follow this link to the APL website
http://aplaudio.com/conc2/products/tda/
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Jack Regula

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Re: APL's Time Domain Analysis - Update?
« Reply #8 on: February 18, 2017, 11:50:07 am »

The TDA 3D display has seductive appeal.  Its just nice to look at, especially when showing a measurement of a good speaker.



An ideal speaker would have a response as shown in the attached figure, the looped back response of a soundcard.  A straight line along the frequency response axis representing the direct sound would indicate perfect time alignment of a multi-way speaker.  The sharpness of this blade would indicate the absence of diffraction and near-in reflections. Delayed reflections would show up as lighter colors to the right of the blade in the area now dark blue.  These are likely to be present in a real room measurement but not in a soundcard loopback.

In TDA, one can choose which time values to display.  I’ve offset the display above by 10 ms. and limited the display range to a 30 ms. range.  Unless offset, time values default to being relative to the arrival of what would be the impulse peak in a conventional IR.  One has the option of connecting a reference loopback via a 2nd soundcard channel if there is a need to know absolute time values – perhaps to compare sound channel latency for various configurations or FIR filters.

The Z-axis defaults to a normalized scale of 0-1 as shown here but can be set into a high dynamic range mode with a logarithmic scale and a configurable maximum value. The normalization sets the amplitude of the direct response line in the 3D display at each frequency to 1. The un-normalized direct response values appear in the AFR graph. 
Just past the 25 ms. mark in this loopback response, you can see a ghostly white line parallel to the frequency axis.  This was determined to be sound card internal crosstalk between its microphone preamp and line level output due to its monitor mixer circuit.  I missed this ghost evaluating the sound card using conventional FR and IR measurements; had I noticed it then I would likely have a different sound card.  With TDA you see things easily overlooked or misunderstood in conventional speaker measurement
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Jack Regula

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Re: APL's Time Domain Analysis - Update?
« Reply #9 on: February 18, 2017, 11:54:44 am »

Now let's look at a real speaker, measuring at a distance of 1m.

A close in measurement is used when the goal is to evaluate a speaker or its crossover.  Some room effects are visible in the 1m measurement shown below but the speaker does dominate.  This is the response of a 3 way, full range speaker with near perfect time alignment and some crossover phase shift evident.  The speaker is nestled tightly into a room corner, eliminating front and sidewall reflections but leaving it susceptible to floor and ceiling reflections that are indeed visible in the display.  Some floor absorption was used near the microphone to limit the disturbance to the midrange response from the floor bounce.  Except for this and some relatively thin carpet, the room is untreated.   Delayed reflections from the back wall of the room are visible near the 38 ms. mark.

Because of the dominance of the speaker over the room modes, TDA correctly identifies the direct response well down into the bass, although the direct response line does widen at lower frequencies.
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