Distortion measurements, THD, IMD-what card?

[fotios]

Rule of thumb:
ADC Dynamic Range (dB) = 6 X bit depth
So:
ADC 8bit D.R. = 6 X 8 = 48dB
ADC 16bit D.R. = 6 X 16 = 96dB
ADC 24bit D.R. = 6 X 24 = 144dB
What could you expect from a Pico? Any sound card of 24bit is unbeatable by any DSO. We have examine this issue of sound cards - enough months ago - on this thread:
http://www.diyaudio.com/forums/solid-state/137843-issues-emu-tracker-thd-measurements.html

Happy new year to all
Fotios

 

[fotios]

This is the performance of an ordinary power amplifier of 170Wrms/8Ohms per channel, captured from an Asus Xonar Essence STX. Settings are 24bit at 48Ks/s. No matters the sampling rate. You can see that the RMS dot line points, almost, at -98dB. How can you obtain this measurement with a Pico of 16bit?

An externally hosted image should be here but it was not working when we last tested it.

 

[AndrewT]

eliminate the test signal peak and then examine the low level remains.
This is the way the old fashioned distortion analysers worked.
Pico could do the same. Filter the output signal to attenuate the test frequency by 60dB and then use 16bit.

How does Cordell's distortion magnifier work?

 

[fotios]

eliminate the test signal peak and then examine the low level remains.
This is the way the old fashioned distortion analysers worked.
Pico could do the same. Filter the output signal to attenuate the test frequency by 60dB and then use 16bit.

How does Cordell's distortion magnifier work?

Andrew, the dot line it shows that the 1KHz fundamental frequency is not included in the measurement. That is indicated by numbers on the top of spectrogram: THD=-88.1dB. Is the second harmonic that, mainly, determines the result of calculation. The issue is that, old fashioned instruments are inadequate according to the possibilities of modern audio electronics. A good example - BTW - are sound cards: you can't find some with THD greater than -105dB. We are not fool to spend our money in useless things.

 

[fotios]

This reply that comes from a constructor of PC based DSOs it could be the better confirmation of what i said:

VT DSO-2815H comes with a hardware bundled Multi-Instrument Standard license, which includes a powerful oscilloscope, spectrum analyzer, and multimeter. It has also a signal generator function which can generate various signals via the sound card. These functions should meet most of your data analysis needs.
Compared with other virtual DSOs in the market, one unique feature is that, in Multi-Instrument, you can use your sound card for audio test and measurement. Audio test and measurements, such as THD, THD+N, SNR measurements, EQ tunning, frequency response measurement, etc.. requires an ADC device with 16-bit or 24-bit resolution. (Note: most of the DSOs in the market are 8-bit or 12-bit ADC device, and is not suitable for these audio measurements due to their limited the dynamic range.)