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Looking for an audio analyzer

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ruairi:
ci11,

Let's not derail the thread by arguing.  I agree with you that anything we can do to help the O.P. understand the issues is useful to him and possibly others.  Again I state that the limiting factor for now will be the O.P.'s understanding of the issues and techniques, not the gear.  Investing is higher end gear makes little sense (and I love high end test gear!).  I don't mean that in a demeaning way at all, I expect that when I finally get my hands on an APx555 I will be the limiting factor too :-)

As far as I can tell, all the DSP I see outlined in both of your examples below is handled in software in a typical sound card based solution.  The hardware tracking analog filter you mentioned was already discussed in a previous post of mine and is part of yielding the higher performance dedicated gear can give.

There are real differences between dedicated audio test gear and bodged together solutions, some of which will matter to the O.P. and some of which may not. The NWavguy blog does a pretty good job of talking through some of these issues - http://nwavguy.blogspot.com

The DIYaudio forum is another great resource.

I agree that quality matters. I pursue it relentlessly in my mastering work, the gear I use, room I work in etc.  I want and need gear that can measure lower levels of distortion, and as you say others will not need that or care.



_Wim_:

--- Quote from: ci11 on January 08, 2017, 07:52:02 pm --- Attached are 2 pictures lifted from AP and R&S literature that describe the front-end processing of their analyzers. These have nothing to do lowering THD+N, that's something different implemented elsewhere.
--- End quote ---

These have almost exclusively to do with improving THD+N. By notching out the test signal (sine), and amplifiing the remaining signal, one can see the lower harmonic distortions much better, because the distortion signals are now amplified, and the test signal is not (otherwise it would be impossible to amplify the input, because the ADC will be overloaded).

If I want to go really low in THD measurements, I do exactly the same by putting Bob Cordell distortion magnifier (http://www.cordellaudio.com/instrumentation/distortion_magnifier.shtml) in front of my sound card. This unit subtracts the test signal from the return signal of the DUT. This distortion magnifier can be bought in a kit from 128 from pilghamaudio (see link at cordellaudio site).

As discussed before, sometimes you need to be a little more creative than having an all in one solution, but very very good results can be obtained using affordable gear. As also said before, the main difficulty is understanding what to measure, and interpreting the result correctly, and the audio precision tools want help in that department

ci11:

--- Quote from: ruairi on January 08, 2017, 08:35:27 pm ---
There are real differences between dedicated audio test gear and bodged together solutions, some of which will matter to the O.P. and some of which may not. The NWavguy blog does a pretty good job of talking through some of these issues - http://nwavguy.blogspot.com


--- End quote ---

Agreed.

The goals dictate the means. With a plethora of available options, many who read these posts do not get a full pictures. Sometimes, it helps to expand, and other times to focus. In this thread, I hope it is clear that there are as many ways to skin the cat as there are opinions, but some very smart people have made important advances to bring more light to the matter. I offered my comments based on this exact spirit.

I wish you well.

ci11:

--- Quote from: _Wim_ on January 08, 2017, 08:36:50 pm ---
These have almost exclusively to do with improving THD+N.


--- End quote ---

Yes, this processing may possibly lower the THD+N of an input signal but its primary purpose is to clean up a "dirty" signal for the ADC before sending it to the DSP for processing. The THD+N improvement circuit for the sine wave output of the internal generator in an APx555 (to lower it from -117db to <-122dB) is a separate matter, and that is what I was referring to.


--- Quote ---
As discussed before, sometimes you need to be a little more creative than having an all in one solution, but very very good results can be obtained using affordable gear. As also said before, the main difficulty is understanding what to measure, and interpreting the result correctly, and the audio precision tools want help in that department

--- End quote ---

Agreed. There is quite a learning curve, and it would be great if analyzers can be rented so those interested can use it on real projects to see if it is their "cup of tea" and it can do their job.

amirm:
THD+N is perceptually blind.  That is, its value does not correlate with how we hear (i.e. ignores masking thresholds).  For that reason I don't use THD analysis in my AP.  Just do a spectrum analysis with the original signal still there and look at the distortions spurs. 

Same thing can be done in software and computer power is superior there to all-in-one-boxes.  The down side is knowing what you are doing with respect to selecting windowing function and such.

BTW, I just met with Prism Sound folks at CES and because of Brexit, they said the retail price has dropped $2000 and you can now buy their analyzer for $6K!  Pretty cheap in my book.  :D

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