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Standard Distortion Spectrum Measurements For Amps (Changstar)

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Marvey:
I figure this might be a good spot for unified measurements for amps or DACs. I'd like to propose a set of measurements standards so we all don't do slightly different things. This keep in mind that let's not go overboard to keep number of measurements small. More measurements, unless well presented = core dump - that even makes my head spin around. Also, like to have meaningful measurements... not a lot of useless random measurements. Presenting noise is just that. Presenting noise.

Please do not comment unless you are one of the regulars who post measurements. In other words, no laymen.

Standard 1kHz distortion spectrum
I suggest loads near 33 ohms and 330 ohm loans.
Any suggestion for Vrms at these two loads? I think we should do a look at volume knob position with real headphones during real listening and start from there. Maybe push up a bit from that position.
I really don't care for this measurement because it seems most gear does well with this test, but it does provide a good baseline.

20Hz single tone distortion spectrum
I suggest loads near 33 ohms and 330 ohm loans.
Any suggestion for Vrms at these two loads?

60Hz single tone distortion spectrum
I suggest loads near 33 ohms and 330 ohm loans.
Any suggestion for Vrms at these two loads?

Two tone 600Hz and 1700Hz distortion spectrum
I suggest loads near 33 ohms and 330 ohm loans.
Any suggestion for Vrms at these two loads? I think we should keep both tones at the same level 1:1 ratio.

Two tone 60Hz and 7000Hz distortion spectrum (a la SMPTE)
I suggest loads near 33 ohms and 330 ohm loans.
Any suggestion for Vrms at these two loads?
Tones at 2:1 ratio for 60hz and 7kHz respectively. (7kHz signal -6db down)


FR
Audio band
Wide band
As far out as possible (limited by sampling rate of ADC and signal generators)


I'd like a three to five tone, but we need to figure that one out. Need a fancy signal generator or wave file.

Donald North:
For the single tone distortion measurements I would try 550mVrms which represents ~1mW into a 300 ohm load. Many dynamic headphones like the HD800 and DT880 250 ohm, for example, are 95-100dB efficient with 1mW of input power. This will be loud on rock music and provide comfortable transient peaks for classical. I would then level match for a popular lower efficiency planar and note that voltage for the 33ohm test. This could be a good starting point.

I also liked your previous choice to test at 40Hz which is a reasonable bass cutoff for a lot of music.

ultrabike:
I've done 1 Vrms and 0.4 Vrms mainly because other folks have done it that way, but 0.55 Vrms is a good and reasonable number going forward.

We could do the classic 19 and 20 kHz CCIF to see abnormal out of band distortion artifacts due to amp near instability or so.

What I do for the voltage on two tones is that I calibrate voltage with a 1 KHz signal (which I also use for THD). Then I do 2 tone while keeping the level constant from where I had it with the THD measurement.

Note the nice thing about SMPTE is that 7000/60 = irrational number meaning that one can separate IMD from THD. So I would suggest something like 600Hz and 1700Hz or similar instead of 500Hz and 1800Hz.

maverickronin:

--- Quote from: ultrabike on July 29, 2015, 09:29:05 PM ---We could do the classic 19 and 20 kHz CCIF to see abnormal out of band distortion artifacts due to amp near instability or so.

--- End quote ---

I second CCIF or something similar.

Donald North:
For the 60Hz/7kHz SMPTE test, shouldn't the ratio be 4:1?

About the 19+20kHz CCIF test, how meaningful is this towards the perceived listening experience? It is interesting from an academic perspective, but does not seem to me to reflect as much a real-world condition as does the 60/7000Hz SMPTE test.

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