ADAU1761 Signal Detection Time_Constant Algorithm
Thread Summary
The user sought the formula for calculating the TimeConstant value for the signal detection block in the ADAU1761, which differs from the ADAU1452. The final answer provided an empirical formula: Param = 1 - 1 / [ (9397 x T) - 1498 ], which is accurate at 2 and 200 seconds. An alternative formula, 1 - 90 / (778871 * x), was also suggested, though it is less accurate for 2 seconds at 48 kHz.AI Generated Content
Hello,
I am using the signal detection block in the ADAU1761, but cannot find any information in the SigmaStudio help, the engineering forum, or the Wiki pages about the actual formula used to generate the time constant value sent to the dsp.
On the ADAU1452 it is a simple matter of multiplying the time_const value by the sample rate, and sending that number of samples to the appropriate detector register.
However, on the ADAU1761, it is not clear what algorithm is being used. The 1452 method does not map to the numbers that show up in the capture window. I have made several attempts to back calculate the formula, but I am missing some key assumption about how the value is calculated. Wiki shows no actual formula, and does not list the different methods for different Sigma devices. I have had to resort to using a table based on the values in the capture window, but this is not very practical for providing user control.
For example, on the 1452, if I enter 2sec in the detection block, the capture window shows 0x17700 (2x48,000=96000 which converts to 0x17700... easy enough).
On the 1761, entering a value of 2sec produces 0x7FFE1B (8388123dec, or 0.9999422 converting to 5.23 format) which is clearly different from the 1452.
One observation is that the 5.23 formatted number get much closer to 1.00000 as the time value approaches its max of 200sec, so maybe that is a clue and it's some kind of percentage of the max, but the math doesn't quite work.
There is a forum entry that lists this issue as answered:
but alas that appears to only satisfy the questioner, and provides no actual formula.
Can someone please provide the actual equation that's used in the SigmaStudio app to generate these TimeConstant numbers? Or provide me a link to where I might find it?
Thanks,
chuck
Audio Signal Processors
adau1452
signal detection
algorithm
time constant
SigmaDSP Audio Processors
adau1761
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Hello Chuck,
This empirical formula is exact at both 2 and 200 seconds, while a bit high in between:
Param = 1 - 1 / [ (9397 x T ) - 1498 ]
This formula seems more accurate: 1 - 90 / (778871*x)
(Though the "2 second" time constant is more like 3.5 seconds in reality, at 48 kHz, so this is only "accurate" in the sense of matching the coefficient to the value displayed in the box.)
Thank you!
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