Bug with "EQ Highshelf" and "EQ Lowshelf" plugins

Russ · Mar 10, 2011, 11:37 AM

There appears to be a bug with some of the coefficient calculations of the "EQ Highshelf" and "EQ Lowshelf" plugins.

It looks like there was a mistake made (with these 2 plugins) with parenthesis in the calculation of "beta", as the plugins' code shows (in 3 places):

Code:

beta = sqrt(TMP*TMP+1)/(eqband/10.)-((TMP-1)*(TMP-1));

AFAIK, it should be:

Code:

beta = sqrt( (TMP*TMP+1)/(eqband/10.)-((TMP-1)*(TMP-1)) );

(from an old version of the Audio EQ Cookbook)

Code:

beta  = sqrt[ (A^2 + 1) /S - (A-1)^2 ]   (for shelving EQ filters only)

[EDIT]
BTW: I thought I should mention that the reason I noticed it is because "EQ Highshelf" was giving unexpected results under some settings (e.g. slope = 2).

Russ · Mar 11, 2011, 01:42 PM

BTW: The range of the Frequency slider for "EQ Highshelf" appears to be off as well. I am not sure what the intended range was (maybe 6000 Hz to 16000 Hz), but it shows 6000 Hz to 27893 Hz (upper limit is over Nyquist... which (I would guess) is not what was intended).

Mar 10, 2011, 11:37 AM	#1
Russ HardwareHeaven Extreme Member Join Date: Jan 2005 Posts: 5,563 Rep Power: 62	Bug with "EQ Highshelf" and "EQ Lowshelf" plugins There appears to be a bug with some of the coefficient calculations of the "EQ Highshelf" and "EQ Lowshelf" plugins. It looks like there was a mistake made (with these 2 plugins) with parenthesis in the calculation of "beta", as the plugins' code shows (in 3 places): Code: beta = sqrt(TMPTMP+1)/(eqband/10.)-((TMP-1)(TMP-1)); AFAIK, it should be: Code: beta = sqrt( (TMPTMP+1)/(eqband/10.)-((TMP-1)(TMP-1)) ); (from an old version of the Audio EQ Cookbook) Code: beta = sqrt[ (A^2 + 1) /S - (A-1)^2 ] (for shelving EQ filters only) [EDIT] BTW: I thought I should mention that the reason I noticed it is because "EQ Highshelf" was giving unexpected results under some settings (e.g. slope = 2). Last edited by Russ; Mar 15, 2011 at 01:50 PM. Reason: more

Mar 11, 2011, 01:42 PM	Thread Starter #2
Russ HardwareHeaven Extreme Member Join Date: Jan 2005 Posts: 5,563 Rep Power: 62	Re: Bug with "EQ Highshelf" and "EQ Lowshelf" plugins BTW: The range of the Frequency slider for "EQ Highshelf" appears to be off as well. I am not sure what the intended range was (maybe 6000 Hz to 16000 Hz), but it shows 6000 Hz to 27893 Hz (upper limit is over Nyquist... which (I would guess) is not what was intended). Last edited by Russ; Mar 11, 2011 at 10:59 PM.