To store high-resolution audio signals efficiently prior to DSD or LPCM delivery the audio data format should have a dynamic range and bandwidth that are substantially greater than the final release form. Simple LPCM would dictate an excessive bit rate. Consequently coding is required that takes account of the normally low ultrasonic content of audio and the inherent high sampling rates. Several strategies are presented, each capable of enhanced resolution, which are benchmarked in terms of bandwidth and spectral noise performance against a 24-bit 88.2-kHz LPCM reference. Candidates include multistage lossless differential coding and sigma-delta modulation (SDM) employing multilevel quantization and parametric noise shaping stabilized using the step-back algorithm. Multilevel SDM and 1-bit SDM are then combined to form a new class of archival format where the output code carries simultaneously both extended resolution data and an exact embedded copy of the 1-bit DSD code. Such a format class is considered a candidate for archiving audio data because not only does it carry audio data with resolution and bandwidth substantially in excess of the LPCM reference but it also retains the DSD release-format data.
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