[Audacity-devel] Equalizer problem - Fixed (mostly)

[<Mar...@ao...>]

 
Hi all,
 
Particularly those interested in the problem with the Equalizer that was  
reported back in April and discussed at length (particularly window  lengths!).
 
I have located the root cause of the problem and why it shows up in  
'Equalizer' but not in 'FFT Filter'.  I believe (and can see) that my  fix also fixes 
the 'Spectrum' view which (I had not reported this as an error  and don't know 
if anybody else had) gives spurious horizontal lines even when  you generate 
a perfect sinusoid.
 
The core of the FFT routine uses 'float' when it should be using 'double'  
(at least). The build up of errors for longer block lengths is significant and  
causes the problems. 'FFT Filter' uses a (hard coded) length of 256, and the  
problems are insignificant whereas 'Equalizer' uses a (hard coded) block 
length  of 16384, which causes significant build up of errors, it would appear.  I  
have not done analysis to find out which of the variables is most significant 
 and boldly changed about 11 of them.
 
I have given more details at _http://members.aol.com/MartynShaw/_ 
(http://members.aol.com/MartynShaw/)  and  a fixed windows exe. I don't mind discussing 
my findings should you have any  queries at all.
 
HTH
 
Martyn
 
PS Are there any other 'signal processing' type bugs/errors/queries  that I 
can get my teeth into?