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Intersample overs in CD recordings

  Monday 27 February 2017, 09:55

Benchmarks Director of Engineering John Siau talks about intersample overshoots that can cause distortion in DA converters.

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 1129 intersample overs. 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 following image shows the track being interpolated with a high-headroom interpolator and a conventional interpolator.

This track can be played cleanly by the Benchmark DAC2 and DAC3 converters. These converters have high-headroom interpolators that accurately render the intersample peaks captured in the recording process. In contrast, conventional converters clip the peaks (as shown with the red markers). In this track the peaks coincide with hits to the snare drum. Converters that clip these peaks add a false brightness to the snare drum and alter its sound. This is just one of the six tracks analysed in this article.

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