High Sample Rate PCM
Posted 2nd May 2016 at 12:13 AM by Tam Lin
Updated 12th July 2016 at 01:38 PM by Tam Lin (corrected typo)
Updated 12th July 2016 at 01:38 PM by Tam Lin (corrected typo)
With delta-sigma DACs pushing insane clock rates I wondered if a traditional multi-bit DAC could not do better. The fastest multi-bit I know of is the PCM1704, which has a max BCLK rate of 25 MHz. A 32-bit sample frame can run at 768 K samples per second. That is fast but not faster than DSD64.
However, with 32 DACs per channel staggered across the sample period we get 24.576 M. That is better than DSD512. For input at or below the native rate of 768K, the DACs operate in parallel. Below the native rate, inserted nulls stretch the output sample period. Above the native rate, the DACs are staggered and the data at each point is the input sample value minus the sum of the data in the other DACs. Thus, each successive sample is the delta needed to reach the next sample point. This approach has interesting repercussions: I will let you ponder them for the time being.
However, with 32 DACs per channel staggered across the sample period we get 24.576 M. That is better than DSD512. For input at or below the native rate of 768K, the DACs operate in parallel. Below the native rate, inserted nulls stretch the output sample period. Above the native rate, the DACs are staggered and the data at each point is the input sample value minus the sum of the data in the other DACs. Thus, each successive sample is the delta needed to reach the next sample point. This approach has interesting repercussions: I will let you ponder them for the time being.
Total Comments 3
Comments
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There's no shortage of multi-bit DACs that go faster than the PCM1704, they just happen not to be targeted at the audio market. AD768 is one such, a fairly ancient design which runs up to 30MHz.Posted 2nd May 2016 at 04:11 AM by abraxalito
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17 bits worth of monotonicity, and uselessly high sample rate, that won't help it ?Quote:This approach has interesting repercussions: I will let you ponder them for the time being.Posted 11th May 2016 at 12:40 PM by tritosine
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Quote:Originally Posted by tritosine
17 bits worth of monotonicity, and uselessly high sample rate, that won't help it ?Above 768K, the DACs handle only the delta, which is typically 5 bits, max 12. In the realm of modern computers, 2^12 is a very small number making it trivial to adjust each and every sample to correct linearity errors.
Posted 8th June 2016 at 08:15 PM by Tam Lin
