BENCHMARK: Audio application notes – Intersample Overs in CD Recordings

John Siau writes:

We have frequently used Steely Dan's Gaslighting Abbie from Two Against Nature in our listening tests. This is a spectacular CD recording with lots of dynamics and a low noise floor. Nevertheless, in a little over 5 minutes, this track has 559 intersample overs on the left track and 570 on the right track for a total of 1129. This means that there are about 3.7 intersample overs per second. The highest intersample over measures +0.8 dBFS. The track itself is not clipped, the 44.1 kHz sampling has simply captured peaks that exceed 0 dBFS. The image above shows the track with the intersample overs highlighted in red.

If we zoom in on this track we can see the what the track should look like without clipping (using a high-headroom interpolator) and we can see what it looks like when rendered with a conventional interpolator (such as those found in most oversampled D/A converters). The vertical red lines have been added to show where clipping occurred in the conventional interpolator.

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