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RE: Also...

1) A decoded HDCD file will only have a maximum number of active bits of 17 in most cases (1 extra bit if Peak Extend (PE) is engaged) or possibly 18 in rare spots in some tracks with extremely quiet passages if both PE and Low Level Extension (LLE) are engaged. (Please remember that PE is always on for the entire disc, while LLE - if engaged - only auto-activates when the peak signal level falls below -45dBFS.) This audio data could be placed into word with lengths anywhere between 18 and 32 bits before being transmitted.

We don't know exactly how dBpoweramp packs the 17- (or sometimes 18-) bit data. The two obvious choices are to pad the LSBs to create either 20-bit words or 24-bit words. I would imagine that 24 is the more likely number. One way to check this would be to compare the file sizes of the undecoded and decoded tracks (taking care to avoid erroneous reporting due to the smallest cluster size created during disk formatting). Also different transport protocols (eg, S/PDIF, USB, Ethernet) may have different word lengths permitted.

2) We don't know exactly how the DAC calculates the reported bit depth. One way would be to count the number of bit clocks per word clock. It is conceivable that this could vary at different points in the DAC's circuitry due to the way that different transmission protocols are decoded. Another way is to simply read the Status Bytes in incoming S/PDIF data. If the professional format is used (as opposed to the consumer format), the source can optionally send data on bit depths for 16, 18,19, 20, 22, 23, and 24 bits - but *not* 17 or 21 bits.

The only thing of which I am confident is that once we understand what is happening, it will all make perfect sense in hindsight... :-)


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  • RE: Also... - Charles Hansen 14:53:09 06/01/17 (0)

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