Originally Posted by Alexey Lukin
I'm talking about the windowed sinc low-pass filter - the most popular type of oversampling filter in D/A converters. It definitely has the ability to increase peak levels of the signal.
thanks for that info. i have been looking at a lot of d/a converters and chips and have not seen that one yet.
but then they didnt have fractals when i went to school.
who would have guessed the cantor set was one.
This was true for non-oversampling DACs, which in fact quite poorly respect the Nyquist theorem (in part of reconstruction accuracy). But nowadays all music DACs are oversampling, and they use low-pass filters in order to comply with a Nyquist theorem. And this is where inter-sample clipping may occur.
i thought all a/d were oversampled.
i need to look more at d/a. have not seen an oversampled one (but maybe it is hidden in the chip).
actually oversampling or not -- with zoh you can filter it any way you want and it cannot peak over the highest sample.
Let me give you an example. Generate the following digital signal at 8 kHz sampling rate:
This is a 2 kHz sine tone digitally peaking at 0 dB FS, but its analog levels go up to +3 dB FS.
er... um..... analog has no FS
its just db below the peak voltage the d/a is designed to use
you cannot legitimately mix the digital and analog domains
Now put your DAC to the test: play this tone. My DAC outputs a pure sine, not clipped. It means that my DAC has the capacity for accommodating at least 3 dB of inter-sample peaks.
mine plays it too. while it ahs the same shape it is smaller and there are no peaks unless I twist the gain knob up.
Now convert (resample) this signal to 44.1 kHz using a decent SRC and let it clip (by saving in a 16-bit format). Here's what you get:
Now listen to it. Clearly, it's different: distorted.
The summary: my DAC can successfully play inter-sample peaks up to 3 dB, but not all DACs are created the same. Some of them may clip on the first waveform. This brings the issue of limiting not only digital levels, but also analog levels (which has been described in many papers by TC Electronic).
I agree that the problem is in the design of the d/a converter but is not due to so called intersample peaks.
I agree that there may be a problem but not that it is the so called interpeak sample caused problem.
It's definitely not a myth, but I'd say that the problem is somewhat over-emphasized. If someone's production is getting rejected because there's an inter-sample peak of +0.9 dB, there may be something wrong with their QA standards or their understanding of dBTP measurements.