SGTL5000 datasheet formula error

cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 

SGTL5000 datasheet formula error

777 Views
erikfriesen
Contributor II

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.

Tags (1)
3 Replies

559 Views
art
NXP Employee
NXP Employee

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

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

559 Views
erikfriesen
Contributor II

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

559 Views
erikfriesen
Contributor II

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.

0 Kudos