Nature of Distortion

[MBK]

BTW since you're using Audiotester too, like me, there is some things I'd like to do haven't found a way how:

- using an external file as a test signal
- real time measurement with peak hold (FFT)

Is it me or does Audiotester just not do these?

(Actually with the soundblaster live card Audiotester exits after a few minutes with access conflicts; works fine with my M-audio external USB soundcard)

[amplifierguru]

Hi MBK,

They still making Robertson amplifiers in Singapore?

Regarding the soundblaster, I have only been toying with it to see what I could extract from it and identifying where the distortions were. Haven't tried the tests you describe. Mine is on Me but can't get the WDM drivers up OR 24bit sampling options.

Can you post your floor?

You have to pay for the AudioTester (28 euros) or it's a trial for 10mins /30 days.

[MBK]

Hi A-G,

don't know about Robertson Amplifiers, I'ver never seen any on stores.

Audiotester:

I did buy the license some time ago because it offers close to the features of, say, Spectraplus, which I liked very much when I tried their demo, at a fraction of the price. But the documentation of Audiotester leaves a lot of things open - for instance I find the interface quite OK but it took me a long time to even find out how to do smoothing of the spectra (in the curves menu). How exactly does it apply FTT windowing, why is this and that not possible, small things, like peak hold, or user test file input. The previously included wave generator did accept file input but you can't link it to the main program, etc etc. Plus, sometimes it does have its own mind. The WDM thing for instance: it seems to depend on the combination of test and FFT values selected, vs. the sampling frequency and bit depth. With some combos it won't accept WDM and then you get problems doing even simple things such as a loopback. In other words, you have to live with a few , err, undocumented featues, for the 28 Euros. But overall I like it given the pricey alternatives.

On my laptop I use the M-Audio pre (USB), and it accepts WDM (most of the time haha) and loopback testing. On the desktop with the Soundblaster Live I couldn't find a way to do a loopback with Audiotester yet. I attach my Soundblaster Live loopback test by RMAA.

First pic, THD 16bit 44.1kHz.

[MBK]

next one, noise 16/44.1

[MBK]

THD 24/96

[MBK]

noise 24/96

[anli]

Hm, it seems like nobody have understood suggested semi-NFB topology :-) Is it so?

OK. Looking at

http://gaydenko.com/um/semiNFB.png

let's imagine R13, R14 have zero resistance values. What do we see? 100% global NFB case. Now, imagine R13, R14 have infinity resistance (or removed at all). Aha, now an output stage is absolutely beyond global NFB loop. And now, you see, the only case isn't imagined when R13, R14 has some not zero and not infinity resistance values. Some _part_ of output stage signal is in global NFB loop as it is reduced with R13-R15 and R14-R15 chains. We have got ... semiNFB!