And for good measure, a 20,000 tone test signal
TD+N = -114dB
Could you zoom way in on that, someplace up high, just to see?
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Multi-tone audio testing?
- Thread starter pkane
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Could you zoom way in on that, someplace up high, just to see?
OP
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No, I don't disagree with that.
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Well if you are creating these multi-tones because people like to think it is more like music, how about having the level go down as the tone goes up. Something like a pink noise shape. Subtract out the tones and compare with what is left. Multi-tone music test.
OP
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- #25
Yes, that's a good idea. Differently or even randomly spaced test tones might be another good test. Something that produces more IMD than the equally (logarithmically) spaced tones.
MRC01
Major Contributor
That make sense to me. Music is likely to have frequencies 100 Hz and lower near full scale, yet never will have frequencies above 4 kHz near full scale. Well, "never" if it is produced from acoustic instruments. With a 2-tone test 19 + 20 kHz, a CD player I used to own (Rotel RCD-1070) measured 30 dB lower distortion when I reduced the test signal from 0 dB to -1 dB. So the frequency vs. amplitude of the test signal definitely changes the distortion profile.
However, there's something to be said for "unrealistic" test signals that are more demanding than anything that music is likely to have. It gives the confidence that your measurements are showing worst-case. If the equipment can handle that, then it can handle music with no problem. It's the opposite of the 1 kHz sin wave test.
It's also quite common if someone is using multitone. A issue is that low frequencies likes to take up headroom so the resolution can be an issue. As low frequency goes higher the different types of distortion is more likely to show. The averaged energy spectrum of music does not represent where the distortion generated. Music is still more dynamic than multitone. It's most likely the transient that causes distortion which is higher frequencies.
So we cannot have a single measurement that tell us all. We still need different types of measurements to fully utilize the test equipment and to fully test out a device.
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That is why I like the twin tone IMD signal. Has steep transients naturally.
I'm in full agreement we need multiple test signals to know a device's capabilities. I don't see big advantages of multi-tone over two tone however. I also think twin tone tells us more than a single tone.
Nothing wrong with that.
The other gorilla in the room is group delay, in that the phase change of the lows and highs as they pass through the DUT. Advancing or retarding the bass can make a big change in overall character of the reproduced audio, harder or warmer sound overall. Just sayin that these days our typical analog chain gear has distortion and noise area well under control.
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OP
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- #32
Is group delay audible in the lower frequencies only? Here's the phase difference plot for that same multi-tone test I posted for Apogee Element. It doesn't appear huge. Is this audible and/or significant?
OP
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- #33
Another multi-tone comparison test.
This time, with the Holo Spring R2R DAC doing the D2A conversion and Apogee Element24 doing the A2D duty. Still at 24/96k:
1kHz single tone:
TD+N = -104dB
11kHz single tone:
TD+N = -90dB
CCIF 18.5k/19.5k two-tone:
TD+N = -90dB
32-tone test:
TD+N = -102dB
500-tone test:
TD+N = -79dB
500-tone test up to 20kHz:
TD+N = -103dB
20k-tone test, phase and frequency response:
Oversample (OS) mode:
TD+N = -65dB
Non-oversample (NOS) mode:
TD+N = -54dB --> 10dB worse than OS mode(!)
Phase:
Frequency response (kinda lumpy, isn't it?):
This time, with the Holo Spring R2R DAC doing the D2A conversion and Apogee Element24 doing the A2D duty. Still at 24/96k:
1kHz single tone:
TD+N = -104dB11kHz single tone:
TD+N = -90dBCCIF 18.5k/19.5k two-tone:
TD+N = -90dB32-tone test:
TD+N = -102dB500-tone test:
TD+N = -79dB500-tone test up to 20kHz:
TD+N = -103dB20k-tone test, phase and frequency response:
Oversample (OS) mode:
TD+N = -65dBNon-oversample (NOS) mode:
TD+N = -54dB --> 10dB worse than OS mode(!)Phase:
Frequency response (kinda lumpy, isn't it?):
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OP
- Thread Starter
- #34
Another test signal (probably not resembling any music anyone ever listens to!)
100Hz square wave, measured using the same method as before with Holo Spring and Element24. Again, white is the distortion+noise, blue is the recorded signal:
Some interesting, high level IMD appears above 40kHz, so let's zoom-in around 45k to see what that looks like:
100Hz square wave, measured using the same method as before with Holo Spring and Element24. Again, white is the distortion+noise, blue is the recorded signal:
Some interesting, high level IMD appears above 40kHz, so let's zoom-in around 45k to see what that looks like:
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The first thing I would try is multi-tones at constant rms level but varying crest factor, and constant crest factor at varying rms level. The problem one runs into is that while these things seem like interesting ideas there is not much around on interpreting the results.
OP
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- #36
Agreed. I implemented a simple crest-factor/phase optimization algorithm in the multi-tone generator. Varying the crest factor and also randomizing or re-distributing the tones in the frequency space could be an interesting comparison. Interpreting the results is really what I'm after with this tool.
Interesting Ray,
Is that a comparison of input and output to your amp and are you confident of the accuracy, do you have a scope or other device to correlate phase shift input vs output, same volts in and same volts out? Would you consider trying at other frequencies up the line to 20Khz please with some other method? This would not be the same in the SET amp world vs solid state.
This 1ms at this frequency is for sure not of any concern imo.
In the audio world, we basically have amplitude, frequency, phase shift, power, and linear and non linear distortion to include noise, and if those areas all look good then the reproduction should be working fine
I would think (not saying I know) that as long as both channels had the same phase shifts then it would not be audible, of course, our hearing of time differences is really superb, so differences in phase between channels in the treble region I would suspect could be detected with a/b testing. this would be imaging for example.
It's an REW measurement sweep and capture with a Focusrite with approximately 5W amp output.
Accuracy is always questionable with single measurement. But it is repetitive, and different when measuring when differences are expected.
I have an old scope but am satisfied with the current result.
Group delay measured at the listening position overwhelms any electrical measurements.
That would be my conclusion.
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Why don't I drag out the scope?
Old Preamp Signal out example
(using 25ft analog cable to PC onboard ADC - power glitch picked up by cable - 1/24 smoothing)
Red - L/R signal sweep, no EQ - similar to amplifier output
Blue - L/R signal sweep with "room correction" for the listening position - will affect amplifier output
Phase:
Nothing faulty there, it's how the "correction" measures, overwhelming any tiny preamp/amp deficiencies.
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