SGTL5000 datasheet formula error

[erikfriesen]

Page 56 of the sgtl5000 datasheet has two formulas for calculating the attack and release rate.  They both don't work for me.

Excel calcs are

#1 = (1-(10^(-(A9/(20*B9))))*2^19) and the result for (A9 or rate_dBs = 32) and (B9 or SYS_FS = 44.1) = -482267 or FFFFF8a425

#1 = (1-(10^(-(A9/(20*B9))))*2^19) and the result for (A9 or rate_dBs = 32) and (B9 or SYS_FS = 1) = -13168 or FFFFFFCC90

Raw formula says (1 - (10^(-(Rate_dBs/(20*SYS_FS)))) * 2^19

Anyway, this formula shouldn't be this complex.  Just give the clock calculations and the math should be straitforward.

[art]

I have checked the formula, it is correct. The point is that the SYS_FS value in the formula should be specified in the units of Hz, not kHz. So, for example, for the sampling rate of 48kHz (48000Hz) and attack rate of 32dB/s the calculation is:

(1-(10^(-(32/(20*48000)))))*524288 = approx. 40.239 = approx. 40 = 0x28

that corresponds to the example value, given in the Data Sheet document.

Have a great day,
Artur

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[erikfriesen]

Well, I suppose I should have tried adding the ')' where you did, but look at the datasheet again, the closing ')' is missing

[erikfriesen]

Just throwing out some guesses

Its an overflow ticker, so

#1 = 0x10000 / Clock * dBsecond

#2 = 0x100000 / Clock * dBsecond

These come out in the ballpark anyway.