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Topic: Pathological example of a intersample peak, 11dB (Read 5121 times) previous topic - next topic

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  • Rescator
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Pathological example of a intersample peak, 11dB
Pathological example of a intersample peak that was artificially created:

~0dB peak, ~20dBFS RMS (squarewave), +10.87dB intersample peak, 44.1KHz, 32bit float.


Discussion thread for this sample: http://www.hydrogenaudio.org/forums/index....showtopic=98753

The red line is 0dBFS, the white line is -1dBFS, even without oversampling one can see the intersample peak is at ~+8.5dBFS, and settles on +10.87dBFS after 2x (or more) oversampling.
  • Last Edit: 09 January, 2013, 10:45:54 PM by Rescator

  • bandpass
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Pathological example of a intersample peak, 11dB
Reply #1
Probably not a big problem for the test you are doing, but your input sample is a bit weird -- not even vaguely symmetrical.  Here's a way to generate a clean input sample:

sox -r 44100 -n InterSamplePeak2.wav synth 220501s 0 25 sin 22050 repeat 1 fade h 5 10 5

  • Rescator
  • [*][*]
Pathological example of a intersample peak, 11dB
Reply #2
Here is a CSV with the result from a scan I did.
The MD5 and CSV was created by a quick tool I made myself, the actual stats was gathered with Sox using the following params. (thanks again bandpass for your sox knowhow).

sox.exe file.wav -n stats upsample 4 sinc -a 40 -t 8k -24k stats

The two stats (peak and rms of the first stats, and the peak from second stats with a +12.04 adjustment to counter the attenuation during the upsampling in sox)

Here follows just one example of the numbers you can do on the attached csv data. Have fun. (PS! the MD5 id is local to the scan/csv file only)
CSV format is: id,peak,rms,isp
peak and rms and isp are all relative to 0 dBFS (0dBFS = +1.0 or -1.0 floating point).


5824 tracks.
Peak -1.18 dBFS (Min -28.03, Max 0.00)
ISP -0.45 dBFS (Min -28.02, Max 9.54)
ISP/Peak Delta -1.63 dB (Min -56.05, Max 9.54)
RMS -16.89 dBFS (Min -46.18, Max -6.34)

27.59% ISP <-1 dBFS
72.41% ISP >-1 dBFS

44.33% ISP -1 to 0 dBFS
19.95% ISP 0 to 1 dBFS
3.71% ISP 1 to 2 dBFS
0.79% ISP 2 to 3 dBFS
0.21% ISP 3 to 4 dBFS
0.34% ISP 4 to 5 dBFS
0.31% ISP 5 to 6 dBFS
1.56% ISP 6 to 7 dBFS
1.18% ISP 7 to 8 dBFS
0.00% ISP 8 to 9 dBFS
0.02% ISP 9> dBFS

  • cloggins
  • [*]
Re: Pathological example of a intersample peak, 11dB
Reply #3
Sigh..... If a DAC, or reconstruction filter, or analog filter or IV converter (or whatever) can't handle valid data within the Nyquist limit, then the DAC is poorly designed. Inter-sample peaking is not a physical law of conversion, it's simply bad conversion design. In a properly designed DAC, at any frequency within the Nyquist limit, a waveform will be properly reconstructed, and a valid MSB clip will give a corresponding analog clip. There is no other "law" governing this, and there is no magic. There are no exceptions to Nyquist's sampling theory.

That said, at sufficiently low levels, a DAC will typically reach its un-dithered linearity limits and the output waveform starts looking like noisy crap. Stereophile tests review DACs at -90dBFS (which is audible), and every single DAC looks terrible, easily 20-30% THD. Personally, I think low-level management is far more important to the "DAC quality" conversation than near-ultra-sonic peak energy that rarely exists in music, and rarely causes a negative listening experience.

If a DAC goes unstable at some high-freq, high-level valid Nyquist state, then the mfr needs to reduce their maximum output specification to a level where this doesn't happen (or ... fix the underlying reason that causes the design instability in the first place). For example, an incoming digital signal would be shifted downward, before the DAC input, until said instability was no longer an issue.
 

  • DVDdoug
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Re: Pathological example of a intersample peak, 11dB
Reply #4
Quote
~0dB peak, ~20dBFS RMS (squarewave), +10.87dB intersample peak, 44.1KHz, 32bit float.
There are no "intersample peaks" in a square wave.   A square wave is square and has one positive an one negative peak-value no matter where you sample it.  Any other peak values in the reconstructed waveform are artifacts.

  • greynol
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  • Global Moderator
Re: Pathological example of a intersample peak, 11dB
Reply #5
There are no "intersample peaks" in a square wave.
Well if you're going to wax philisophical, you cannot create an actual square wave through discrete-time sampling.

Any other peak values in the reconstructed waveform are artifacts.
Artifacts of BW limiting; which is a requirement to prevent aliasing from the A/D side and imaging on the D/A side.

A sampled square wave will have ringing as a result of bandwidth limiting.  Unless the stars are perfectly aligned, inter-sample overs are guaranteed.
  • Last Edit: 01 August, 2017, 04:25:27 PM by greynol
Is 24-bit/192kHz good enough for your lo-fi vinyl, or do you need 32/384?

Re: Pathological example of a intersample peak, 11dB
Reply #6
@greynol and DVDdoug
20dBFS RMS (squarewave) refers to the RMS measurement not the waveform. Depending on the software used there may be a RMS (squarewave) or a RMS (sinewave) option when getting the RMS (in this case Adobe Audition 3 was used)

@cloggins
This is in no relation to any DAC. A (extreme) test sample was needed as a reference for a ISP scan of a music collection https://hydrogenaud.io/index.php/topic,98753.0.html
This was kept separate from this thread as it was assumed that the test sample might be of use beyond just that thread.