DSP block parameter definitions
I am currently writing code for controlling an ADAU1442 DSP, and have had no luck finding detailed documentation describing the various registers. I've found documentation of the basic fixed point formats used, but nothing describing the function, valid range, units, or any special values of the various register settings. Is there more complete documentation somewhere?
I did find a document describing the fixed point and integer formats, which throws out one confusing mention that 8388608 (that is, 1 << 23) is "0 dB full scale represented in 28.0 format". I'm interpreting that to mean that the value 8388608 in the 28.0 format is 1 in the 5.23 format, and that parameters and signals are represented as linear values, not logarithmic...gain parameters, for example, would be simple multipliers in 5.23 fixed point format, not decibels. Is this correct?
Audio Signal Processors
adau1442
SigmaDSP Audio Processors
Hello,
Yes, often SigmaStudio converts gains entered as dB to linear coefficients for the DSP. For example, the filter shown at left is set to flat, so it has only one nonzero coefficient equal to its linear gain. When I enter 6 dB (linear gain of 2) into the filter's gain box, the Capture Window updates the linear coefficient to 2.0.
Your understanding of the 5.23 number format is also correct. 1.0 in 5.23 format is 8388608 (base 10) in integer format. This is demonstrated below:
Thus, linear gains are easily done. Parameters for more complex functions vary according to how the blocks function. Some info is available here:
Algorithm Information [Analog Devices Wiki]
A spreadsheet giving EQ filter parameters is here (scroll down a ways):
EQ Low- and High-Shelf filter coefficients comming back - Mysterious S factor.
A useful tutorial on preparing parameters to load into the DSP is here:
https://ez.analog.com/message/231031#comment-231031
Best regards,
Bob
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