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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => Audio Measurement and Testing => Topic started by: David Junius on September 07, 2020, 10:32:28 pm

Title: Smaart or?
Post by: David Junius on September 07, 2020, 10:32:28 pm
I understand Smaart is probably the most common software everyone is using but I know thereís others out there. Iím hoping to invest in a system once I can start working again, so I figure in the meantime I would research what to buy. I realize thereís a learning curve Iíll have to get over no matter which software I go with. Iíll need a new computer and an interface box, Iíve already got an earthworks mic. So whatís everyoneís favorite FFT software and whoís near Atlanta that can help me learn how to use it?

Thanks,
David
Title: Re: Smaart or?
Post by: Chris Grimshaw on September 08, 2020, 03:06:25 am
I use REW, but you do have to run sine sweeps to get all the data (harmonic distortion, waterfall, etc). It also has an RTA built-in, but it's single-channel. ie, it'll tell you what's coming in on that input, but the dual-channel FFTs (Smaart etc) will compare that input to another, resulting in a transfer function. In theory, any signal (including, I suppose, the output of the FOH desk) could be used to make that transfer function, which gives additional flexibility.

Chris
Title: Re: Smaart or?
Post by: Michael Lawrence on September 08, 2020, 10:37:06 am
I understand Smaart is probably the most common software everyone is using but I know thereís others out there. Iím hoping to invest in a system once I can start working again, so I figure in the meantime I would research what to buy. I realize thereís a learning curve Iíll have to get over no matter which software I go with. Iíll need a new computer and an interface box, Iíve already got an earthworks mic. So whatís everyoneís favorite FFT software and whoís near Atlanta that can help me learn how to use it?

Thanks,
David

David -

Full disclosure - I'm a Smaart trainer.

Although each particular software platform has a learning curve, for sure, a lot of the work to be done is learning how to interpret the data (Live Impulse Response, Magnitude, Phase, and Coherence are the mainstays of a modern dual-channel audio analyzer). That data itself is platform agnostic, which means whether I'm looking at Smaart, SysTune, SIM, SpectraFoo, or whatever, I am still more or less parsing the same data the same way as a basis for my decisions. (REW is a little different, in that it's a non-realtime swept measurement platform and so can't produce a coherence trace or Live IR.)

So there is great value in learning the underlying measurement theory concepts regardless of which platform you end up using, and that's all covered in the free Smaart Operator Fundamentals Online webinar series which you can check out here (https://www.youtube.com/user/RationalAcoustics/playlists). If you're like me and you prefer reading to watching, the Smaart v8 manual also does a very good job explaining the general concepts as well.

I'll also add that most of the major players in the dual-channel FFT analyzer scene offer free trial periods, so I encourage you to take full advantage of those offers, try a bunch of different platforms and decide for yourself which is the best fit for your needs.
Title: Re: Smaart or?
Post by: John Schalk on September 08, 2020, 11:30:46 am
If you go to the first link below and select on SOFTWARE in the header, you'll get a pretty comprehensive list of all of the options that are out there.  By selecting one of the options, it will bring up some information about the app and some links.  These pages are a little dated, but the only app that I am aware of that isn't on the list is Open Sound Meter.  REW has a ton of help docs and a very active user forum, although it is heavily weighted to home theater use cases.  From what I have observed, most labsters are Smaart!

http://www.audiomeasurements.com/?p=4048

https://opensoundmeter.com/
Title: Re: Smaart or?
Post by: David Junius on September 08, 2020, 11:44:00 am
David -

Full disclosure - I'm a Smaart trainer.

Although each particular software platform has a learning curve, for sure, a lot of the work to be done is learning how to interpret the data (Live Impulse Response, Magnitude, Phase, and Coherence are the mainstays of a modern dual-channel audio analyzer). That data itself is platform agnostic, which means whether I'm looking at Smaart, SysTune, SIM, SpectraFoo, or whatever, I am still more or less parsing the same data the same way as a basis for my decisions. (REW is a little different, in that it's a non-realtime swept measurement platform and so can't produce a coherence trace or Live IR.)

So there is great value in learning the underlying measurement theory concepts regardless of which platform you end up using, and that's all covered in the free Smaart Operator Fundamentals Online webinar series which you can check out here (https://www.youtube.com/user/RationalAcoustics/playlists). If you're like me and you prefer reading to watching, the Smaart v8 manual also does a very good job explaining the general concepts as well.

I'll also add that most of the major players in the dual-channel FFT analyzer scene offer free trial periods, so I encourage you to take full advantage of those offers, try a bunch of different platforms and decide for yourself which is the best fit for your needs.

Michael,
First off, thanks, your reply makes perfect sense and I didnít think of it like that. Iím basically new to FFT measurements, however Iíve seen Smaart in use before with impulse response measurements for setting up EQís and crossovers but donít feel I could interpret the data it yields by myself. Iím aware of the Smaart free trial but I need to get a new computer and some sort of box for input and outputs. And Iíll definitely check out that link you provided!

I know Iím looking for a program to do impulse response measurements but as far as the live aspect, Iím not as familiar with what data I can view for that and what to do with that data once Iíve got it, but Iím sure once I start learning it will become clear.  So with that being said, I guess my question becomes does a particular software have more of a market place, as in is one brand more popular with the masses of users? My guess is that Smaart would be that choice but the audio folks on my level donít seem to be using measurement software near me so I canít really get a valid answer locally. Thanks again.

David
Title: Re: Smaart or?
Post by: David Junius on September 08, 2020, 11:50:30 am
If you go to the first link below and select on SOFTWARE in the header, you'll get a pretty comprehensive list of all of the options that are out there.  By selecting one of the options, it will bring up some information about the app and some links.  These pages are a little dated, but the only app that I am aware of that isn't on the list is Open Sound Meter.  REW has a ton of help docs and a very active user forum, although it is heavily weighted to home theater use cases.  From what I have observed, most labsters are Smaart!

http://www.audiomeasurements.com/?p=4048

https://opensoundmeter.com/

Wow John,
Thatís quite a link. I have a feeling Iíll be stuck on that site for awhile! Thanks!

David
Title: FFT Windowing
Post by: Doug Fowler on September 08, 2020, 12:49:59 pm


Although each particular software platform has a learning curve, for sure, a lot of the work to be done is learning how to interpret the data (Live Impulse Response, Magnitude, Phase, and Coherence are the mainstays of a modern dual-channel audio analyzer). That data itself is platform agnostic, which means whether I'm looking at Smaart, SysTune, SIM, SpectraFoo, or whatever, I am still more or less parsing the same data the same way.......

It's all good until windowing is applied.   SysTune is extremely powerful but the user still has to choose to make a windowed or unwindowed measurement.   And the user must choose the windowing parameters.

A few years back a (very) controlled test was done between five analyzers.  Each produced identical results for unwindowed measurements (I would hope so...) but when windowing is applied, basically five different results are produced. 
Title: Re: Smaart or?
Post by: Michael Lawrence on September 08, 2020, 12:54:07 pm
Michael,
First off, thanks, your reply makes perfect sense and I didnít think of it like that. Iím basically new to FFT measurements, however Iíve seen Smaart in use before with impulse response measurements for setting up EQís and crossovers but donít feel I could interpret the data it yields by myself. Iím aware of the Smaart free trial but I need to get a new computer and some sort of box for input and outputs. And Iíll definitely check out that link you provided!

I know Iím looking for a program to do impulse response measurements but as far as the live aspect, Iím not as familiar with what data I can view for that and what to do with that data once Iíve got it, but Iím sure once I start learning it will become clear.  So with that being said, I guess my question becomes does a particular software have more of a market place, as in is one brand more popular with the masses of users? My guess is that Smaart would be that choice but the audio folks on my level donít seem to be using measurement software near me so I canít really get a valid answer locally. Thanks again.

David

The mainstays of live sound system alignment work are the frequency-domain data (Magnitude, Phase, Coherence) as well as the live Impulse Response. It is no coincidence that Smaart's Transfer Function view shows all four of these by default.

You should understand (and this is covered well in all the resources I mentioned above) that the frequency-domain data (Magnitude, Phase) and the time domain data (Impulse Response) are literally the same data. The FFT and its brother, the IFFT, are what allows the analyzer to convert the raw measurement data back and forth. It's initially gathered in the time domain (a waveform that you capture with a microphone or an interface is amplitude over time) but the form in which we choose to view the data depends on what we're trying to learn about. Generally speaking, the "bread and butter" of sound system measurement / alignment / optimization work is driven by viewing the data in the frequency domain (Magnitude / Phase), whereas acousticians, who are more concerned with the acoustic properties of the room itself, tend to study Impulse Response data which allows them to see how the energy decays with time. But, the power of a modern audio analyzer means we don't usually have to pick and can indeed view the same data both ways, in some cases simultaneously.

All that is likely putting the cart a bit before the horse, but the takeaway is that as you learn how to interpret the different types of measurement plots and understand what they mean, you will be able to choose what you need to accomplish the task at hand. (In other words, an analyzer is not just a single tool, it's more like a tool kit, it does lots of things, and the key is knowing what particular tools you need for what you're trying to accomplish.)

The most three common measurement platforms you're likely to encounter on a show site would probably be Smaart, SysTune, and Tuning Capture, in that order, but I don't have nearly enough "drive time" with the latter two platforms to make any helpful statements. To quote bassist Victor Wooten, "gear is like clothing. Use what's comfortable." You're pulling out an analyzer on site to get the answer to a question, so ultimately I would say it's about choosing a tool that has the capability to answer that question, andbecoming good enough at using the tool to get results in a timely fashion. That's where workflow, featureset, etc come into play. The underlying math that drives these analyzers is 200 years old, so in the general sense there's nothing newfangled or proprietary happening. All of these tools will give you pretty much the same answer if you ask the question properly.
The only caveat would be that a swept measurement system tends to be a bit less than optimal for our uses in the live sound world, primarily due to the inability to take a real-time measurement using any source material. I would also posit that customer support and training may well factor into your cost/benefit analysis, particular as a new user.
Title: Re: FFT Windowing
Post by: Michael Lawrence on September 08, 2020, 12:56:40 pm
It's all good until windowing is applied.   SysTune is extremely powerful but the user still has to choose to make a windowed or unwindowed measurement.   And the user must choose the windowing parameters.

A few years back a (very) controlled test was done between five analyzers.  Each produced identical results for unwindowed measurements (I would hope so...) but when windowing is applied, basically five different results are produced.

For sure, Doug. Add into the equation that most modern dual-channel platforms are using some form of Fixed-PPO, plus the variation of averaging, smoothing, and banding algorithms and you are very well down the path of why certain platforms "feel" different. And the real fun begins once you allow for the fact that smoothing in the frequency domain can use used to give the same result as windowing in the time domain.... :o
Title: Re: Smaart or?
Post by: Mark Wilkinson on September 08, 2020, 01:31:13 pm
I use Smaart and REW both, quite a bit really, as a system tuner and avid DIY speaker builder.
Also spent a little time with Systune and ARTA.

Michael's comments are spot on imo, regarding the value in learning the underlying measurement theory concepts.
All the manuals for the products I just mentioned are great resources for that.
For me, the Smaart manual, and the REW help files have been my go-to sources of info. 
Would also add I've taken three Smaart training sessions, and could no doubt use at least three more  ;)
I think the recently produced Smaart youtubes are an awesome and generous resource.

Many folks start with REW because it is donate-ware and has a big group of users in home-theatre and DIY. 
And it's quite good with an array of "bench-type" testing and analysis capabilities, like harmonic distortion, CEA2010 max SPL testing. Also has very useful trace arithmetic, and a number of other assorted features.

For me, there is a huge difference in a single channel program like REW, and a dual channel like Smaart.
The biggest pluses to me are real time measurements, temporal and spatial averaging, and coherence as already mentioned.

Here's an example of how that helps....
As I type this, I've got a new speaker project out on my deck overlooking a large lake.  There is so much dang noise you'd think it would be impossible to make any measurements.  Boats, jetskis, waves slapping the shore...and circadias about as loud as anything. Heck, next door neighbor is mowing grass and reads 80dB at my test mic.

But look at the magnitude trace of a high frequency driver under test.  It is repeatable without significant variation despite all that noise.
The key being the 2 second temporal averaging.
I'd never try to use REW is this noisy situation....the sine sweep can't average.

Another cool thing about real time, is that you can see effects of EQ as you "twist knobs".  Single channel demands you make changes, check them, make changes again, check again...etc etc.

Anyway, all that said about a strong preference for dual channel, it still comes down to what are you trying to do....
Good luck !

edit:  my dumb ass forgot to include attachment
Title: Re: FFT Windowing
Post by: Mark Wilkinson on September 08, 2020, 01:42:12 pm
It's all good until windowing is applied.   SysTune is extremely powerful but the user still has to choose to make a windowed or unwindowed measurement.   And the user must choose the windowing parameters.

A few years back a (very) controlled test was done between five analyzers.  Each produced identical results for unwindowed measurements (I would hope so...) but when windowing is applied, basically five different results are produced.

That's what turned me off about Systune...the need to use windowing at times vs not at others. 
Imho, I believe Systune has fallen behind with the trend to build in some type of fixed-PPO scheme, to solve its windowing requirement.

I've compared Smaart and REW many times using default settings, and they always appear spot-on with each other.
My hope is there has been similar convergence with most other measurement programs.
Title: Re: Smaart or?
Post by: Chris Grimshaw on September 09, 2020, 05:05:44 am

I'd never try to use REW is this noisy situation....the sine sweep can't average.


Actually, if you run multiple sweeps under the same measurement (there's a drop down - 1,2,4,8), REW looks at the correlated data, thus discarding background noise.

As an interesting example, I've measured a speaker that was inaudible in-room. I used a Beyerdynamic MC930 positioned close to the speaker, and ran sweeps at decreasing levels until I couldn't hear the sweeps any more. I was sat at around 0.5m from the speakers. It was an investigation into what happens when speakers are used very close to their zero-point, and the answer is "nothing unexpected - they just get quieter".

I usually use 2-4 sweeps in most situations, 1x for electrical loop-through and 8x when there are noise problems.

I should probably get around to Smaart for the Armonia+ integration if nothing else, but the pricing is prohibitive at the moment.

Chris
Title: Re: Smaart or?
Post by: Mark Wilkinson on September 09, 2020, 11:58:31 am
Actually, if you run multiple sweeps under the same measurement (there's a drop down - 1,2,4,8), REW looks at the correlated data, thus discarding background noise.



Yep, I've used the multiple sweep option many times.....works great.  There's so much to like about REW. 
Heck, the excellent trace arithmetic and windowing export capability can even generate FIR filters (via simple impulse inversions).

But, the annoyance of multiple sine sweeps whooooooping it up gets me in trouble with nearly everybody,......... at home, in the neighborhood, or at an installation or gig site.
Whereas nobody seems to mind some steady pink noise.
Title: Re: FFT Windowing
Post by: David Junius on September 09, 2020, 11:59:35 am
It's all good until windowing is applied.   SysTune is extremely powerful but the user still has to choose to make a windowed or unwindowed measurement.   And the user must choose the windowing parameters.

A few years back a (very) controlled test was done between five analyzers.  Each produced identical results for unwindowed measurements (I would hope so...) but when windowing is applied, basically five different results are produced.

Ok, I was following along fine until you brought up windowed and unwindowed measurements. Iíve been researching on the links provided so Iíll see if I can figure that out! I feel this subject area goes from the kiddie pool area to 20,000 leagues real fast but Iíll get there one day!

David
Title: Re: Smaart or?
Post by: Dave Garoutte on September 09, 2020, 12:43:42 pm
Whereas nobody seems to mind some steady pink noise.
Plus you can mix in some recorded music with the pink.
It's way less annoying and works perfectly.
Title: Re: Smaart or?
Post by: Tim McCulloch on September 09, 2020, 02:30:31 pm
For those playing along at home and wondering what the talk of windows is about:

https://en.wikibooks.org/wiki/Digital_Signal_Processing/Windowing
Title: Re: FFT Windowing
Post by: Russell Ault on September 09, 2020, 03:14:24 pm
[...] And the real fun begins once you allow for the fact that smoothing in the frequency domain can use used to give the same result as windowing in the time domain.... :o

Wait, what? How does that work?

-Russ
Title: Re: FFT Windowing
Post by: Michael Lawrence on September 09, 2020, 04:37:43 pm
Wait, what? How does that work?

-Russ

In broad, non-mathematical strokes:
Shorter time window = lower frequency resolution, suppresses influence of late arriving energy.
Frequency domain smoothing = lower frequency resolution, suppresses influence of late arriving energy.

Fine print: it must be complex smoothing, and it must be linear frequency smoothing, not fractional octave smoothing as is far more common. Without going too far down a very tedious rabbit hole, frequency-domain smoothing can give you a comparable result at HF while avoiding the LF data point loss that comes with time-domain windowing. There's actually a "hidden" feature in v8 that exists pretty much only to demonstrate this point: in Transfer Function options, check "Enable FTW" under "Advanced." That enables "Frequency-Domain Time Windowing", which is a frequency-domain linear complex smoothing function that's mathematically equivalent to windowing in the time domain. Input the half-window length in ms into the FTW field in the TF control bar, and you can compare that against a measurement taken without the setting but using "regular" smoothing, and also to a time-windowed measurement taken in IR mode if you choose. Details here (https://www.rationalacoustics.com/download/Smaart-v8.3-Release-Overview.pdf), pages 6-8.
Title: Re: Smaart or?
Post by: Mark Wilkinson on September 09, 2020, 05:01:48 pm
Plus you can mix in some recorded music with the pink.
It's way less annoying and works perfectly.

Heck yeah, works great !!

Speaking of annoyances....i found even when using music with background pink as the reference....
..when my habit was i'd turn the whole music/pink caboodle mix on & off  when making measurements....

that a number of people have come up to me and said "would you please let the songs play through without turning them off?"

So now i just keep music playing continually during all measurements..
Title: Re: FFT Windowing
Post by: Frank Koenig on September 09, 2020, 05:04:27 pm
And the real fun begins once you allow for the fact that smoothing in the frequency domain can use used to give the same result as windowing in the time domain.... :o

In rough terms, yes, but it depends. Multiplication by a function, such as a window, in one domain (time or frequency) is equivalent to convolution by the Fourier transform of that function in the other domain. A window, by definition, is of finite length (zero outside some range) so its Fourier transform has ripples that go out to infinity, which may not be the best smoothing kernel. (This is a manifestation of the Gibbs Phenomenon.) Furthermore, in audio, we often like frequency-domain smoothing to be frequency-proportional (such as 1/6 octave). Multiplication of the impulse response by a window results in constant-frequency smoothing (such as 100 Hz).

The most common reason for windowing the impulse response is to remove reflected sound so as to achieve a pseudo-anechoic measurement. The goal is to include as much of the direct sound as possible without causing excessive artifacts in the frequency response due to the sharpness of the window's edges. This is at odds with good smoothing.

I believe what Smaart does in "MTW" mode is to apply longer windows to lower frequencies to allow greater frequency resolution (in Hz, not octaves) at those frequencies at the expense of including more reflected sound.

Smaart is great for quick-and-dirty measurement in the field -- system health, sub alignment, and so forth. It's also nice for what I might call acoustic exploration where you move things around and can immediately see the effect. For detailed speaker measurements under more controlled conditions, as well as room acoustic measurements, where you really want to know what you're getting, I think there are better tools.

--Frank
Title: Re: FFT Windowing
Post by: Mark Wilkinson on September 09, 2020, 05:11:42 pm
In broad, non-mathematical strokes:
Shorter time window = lower frequency resolution, suppresses influence of late arriving energy.
Frequency domain smoothing = lower frequency resolution, suppresses influence of late arriving energy.

Fine print: it must be complex smoothing, and it must be linear frequency smoothing, not fractional octave smoothing as is far more common. Without going too far down a very tedious rabbit hole, frequency-domain smoothing can give you a comparable result at HF while avoiding the LF data point loss that comes with time-domain windowing. There's actually a "hidden" feature in v8 that exists pretty much only to demonstrate this point: in Transfer Function options, check "Enable FTW" under "Advanced." That enables "Frequency-Domain Time Windowing", which is a frequency-domain linear complex smoothing function that's mathematically equivalent to windowing in the time domain. Input the half-window length in ms into the FTW field in the TF control bar, and you can compare that against a measurement taken without the setting but using "regular" smoothing, and also to a time-windowed measurement taken in IR mode if you choose. Details here (https://www.rationalacoustics.com/download/Smaart-v8.3-Release-Overview.pdf), pages 6-8.

Michael, I think of gating and widowing as two different animals.
Windowing, i think of as how to handle the FFT block sizes being used for the mathematical computations...the stuff Calvert does that makes my head swim.
Gating, on the other hand, i think of as 'how long a time period will i let the measurement analyze'......and watch Jamie want to start cussing when it's brought up lol.

In the end, i guess frequency smoothing, gating, widowing .....all throw away data and look smoother.  Hopefully for good reasons.
Pls feel free to correct my thinking  :)
Title: Re: FFT Windowing
Post by: Russell Ault on September 09, 2020, 05:13:40 pm
[...] Fine print: it must be complex smoothing, and it must be linear frequency smoothing, not fractional octave smoothing as is far more common. [...]

...that was the part I was missing. Makes sense!

-Russ
Title: Re: FFT Windowing
Post by: Mark Wilkinson on September 09, 2020, 05:31:13 pm

I believe what Smaart does in "MTW" mode is to apply longer windows to lower frequencies to allow greater frequency resolution (in Hz, not octaves) at those frequencies at the expense of including more reflected sound.

Smaart is great for quick-and-dirty measurement in the field -- system health, sub alignment, and so forth. It's also nice for what I might call acoustic exploration where you move things around and can immediately see the effect. For detailed speaker measurements under more controlled conditions, as well as room acoustic measurements, where you really want to know what you're getting, I think there are better tools.

--Frank

Hi Frank, i think the MTW mode does allow greater frequency resolution down low, but at the same time minimizing reflected noise as frequency increases....iow, different time windows (perhaps i should say different effective gating vs freq).

I used to think better detailed speaker measurements could be gained with better tools than Smaart.
But speakers and room acoustics appear to be so coarse and so variable ..orders of magnitude grosser in their ability to perform or provide repeatable measurements .....
....than Smaart or any decent measurement program can provide given a constant stimulus ..
....that i'm being led to believe very fine measurements are pretty much point-in-time, point-in-space.... BS.
Title: Re: FFT Windowing
Post by: Frank Koenig on September 09, 2020, 05:33:09 pm
More generally, we can think of there being three parts to this problem.

First is getting the best possible estimate of the system function (transfer function) subject to the noise and non-stationarity of the given measurement environment. This affects the choice of test signal (sine-sweep, pseudo-noise, easy jazz) and the estimation algorithm. The result is an impulse or (equivalently) complex frequency response.

Second is extracting the relevant parts, such as windowing out reflections, averaging multiple measurements, and smoothing. This blends into the third, which is representing the data in a perceptually meaningful way for the problem at hand, such as log-magnitude and phase plots, minimum phase and excess phase parts, group delay, and various time-frequency-energy representations. This last bit is very open ended.

--Frank
Title: Re: FFT Windowing
Post by: Frank Koenig on September 09, 2020, 05:50:35 pm
Hi Frank, i think the MTW mode does allow greater frequency resolution down low, but at the same time minimizing reflected noise as frequency increases....iow, different time windows (perhaps i should say different effective gating vs freq).

I used to think better detailed speaker measurements could be gained with better tools than Smaart.
But speakers and room acoustics appear to be so coarse and so variable ..orders of magnitude grosser in their ability to perform or provide repeatable measurements .....
....than Smaart or any decent measurement program can provide given a constant stimulus ..
....that i'm being led to believe very fine measurements are pretty much point-in-time, point-in-space.... BS.

Not disagreeing. And Smaart does a good job. I just have a little trouble with their lack of transparency about what it's doing. It strikes me a bit dumbed-down. At least with ARTA it's all spelled out, it's easy to export the data, and the built-in analysis tools are good and I can check my own stuff against them. (And I've plagiarized from their manual ;) ) --Frank


Title: Re: FFT Windowing
Post by: Michael Lawrence on September 09, 2020, 06:35:37 pm
I just have a little trouble with their lack of transparency about what it's doing. It strikes me a bit dumbed-down.
Frank, can I ask what you feel is not transparent? Happy to help shed some light. MTW is no trade secret, Jamie spends quite a bit of time on it in class so people know exactly what it does (and thanks to COVID-19 that is on YouTube as well). See the attached image, courtesy of Merlijn, for a run-down on the time records in MTW.

Since you're more of an under-the-hood guy, you can also right-click any saved measurement to dump the measurement data into ASCII, drop that into Excel or program-of-your-choice and confirm the time windows yourself if you like.

But seriously, if you have questions, feel free to give Calvert a buzz - he loves to talk about that stuff and now that we're all working remotely, he's got no one to talk to about it  ;D  Happy to connect you.
Title: Re: FFT Windowing
Post by: Frank Koenig on September 09, 2020, 07:16:28 pm
Frank, can I ask what you feel is not transparent? Happy to help shed some light. MTW is no trade secret, Jamie spends quite a bit of time on it in class so people know exactly what it does (and thanks to COVID-19 that is on YouTube as well). See the attached image, courtesy of Merlijn, for a run-down on the time records in MTW.

Since you're more of an under-the-hood guy, you can also right-click any saved measurement to dump the measurement data into ASCII, drop that into Excel or program-of-your-choice and confirm the time windows yourself if you like.

But seriously, if you have questions, feel free to give Calvert a buzz - he loves to talk about that stuff and now that we're all working remotely, he's got no one to talk to about it  ;D  Happy to connect you.

Michael, thank you so much. I clearly need to revisit the Smaart material that's available now.

I never saw that table before but maybe I just didn't look hard enough. It certainly shows the bands, much as I suspected. I bet they correspond to the steps you see in the coherence plot when you have the delay setting way off.

In fairness, I suppose Rational makes money off the training so they don't want to give away all the jewels in a super-complete manual. And I appreciate the easy-to-use aspect. There's no reason for most folks to have to worry about a lot of settings that don't make much difference in their day-to-day audio testing.

--Frank


Title: Re: FFT Windowing
Post by: Michael Lawrence on September 09, 2020, 07:51:45 pm
Michael, thank you so much. I clearly need to revisit the Smaart material that's available now.

I never saw that table before but maybe I just didn't look hard enough. It certainly shows the bands, much as I suspected. I bet they correspond to the steps you see in the coherence plot when you have the delay setting way off.

In fairness, I suppose Rational makes money off the training so they don't want to give away all the jewels in a super-complete manual. And I appreciate the easy-to-use aspect. There's no reason for most folks to have to worry about a lot of settings that don't make much difference in their day-to-day audio testing.

--Frank

No problem, Frank. Most of this info is 'free for the asking' to interested parties - very, very little is actually proprietary in terms of number crunching. It's just that, exactly as you stated - for the vast majority of users, there is no interest or desire (or need) to learn it at that level. It's about getting actionable results quickly - how to use the MRI machine rather than how to build one. That being said, there are a lot of hidden "tweakhead" things in there if you know where you look ;)

m

EDIT: And, yes, exactly, the stairstep drops in coherence with wrong measurement delay show the "edges" of the time records. If you dump the data into Excel and subtract adjacent frequency points, you can see exactly where the seams are.