Alex Stahl

I am suffering from "patcher's block" (like writer's block) looking 

for a way to graph fft amplitude frames on a log frequency scale. 

Spectrograph~ is almost, but not quite, what I need for this patch. 

Using the vectral~ help file as a starting point, I thought maybe 

warping the signal going from the fft ramp outlet to vectral~'s index 

inlets would work, but I couldn't find documentation about those 

inlets and my experiments didn't seem to work. There must be an 

obvious approach I am missing...any ideas, examples, or other 

thoughts to help get me un-stuck on this?

I am suffering from "patcher's block" (like writer's block) looking  
for a way to graph fft amplitude frames on a log frequency scale.  
Spectrograph~  is almost, but not quite, what I need for this patch.  
Using the vectral~ help file as a starting point, I thought maybe  
warping the signal going from the fft ramp outlet to vectral~'s index  
inlets would work, but I couldn't find documentation about those  
inlets and my experiments didn't seem to work. There must be an  
obvious approach I am missing...any ideas, examples, or other  
thoughts to help get me un-stuck on this?

log-frequency-graphing

Well, if you're working in pfft~, and you don't have to worry about 

the mirror image at the top of your fft, just use log~, and then rescale 

log~'s output to your frame size. For example, if your fft index (the 

third output from fftin~) goes from 0-256, that means that log~'s output 

will go from 0-8 (using the default base 2). Then multiply that signal 

by 32 to get you back to your original frame size, but now you've 

log-scaled your frequency. Use that signal as the middle input to 

vectral~. The left input signal can just be your ordinary, unaltered 

If you are using fft~ rather than pfft~, you'll need to split up your 

index signal into its two halves and do a little math on the mirror 

filter out the zeros going to your log~ object!

Hi Alex,
  Well, if you're working in pfft~, and you don't have to worry about 
the mirror image at the top of your fft, just use log~, and then rescale 
log~'s output to your frame size.  For example, if your fft index (the 
third output from fftin~) goes from 0-256, that means that log~'s output 
will go from 0-8 (using the default base 2).  Then multiply that signal 
by 32 to get you back to your original frame size, but now you've 
log-scaled your frequency.  Use that signal as the middle input to 
vectral~.  The left input signal can just be your ordinary, unaltered 
index output from the fftin~.
  If you are using fft~ rather than pfft~, you'll need to split up your 
index signal into its two halves and do a little math on the mirror 
image part.
  Other tips:
    filter out the zeros going to your log~ object!
    experiment with different log bases

What about the logarithmic option in the Spectrograph~ object's option 

dialog isn't working for you? What else do you need it to do?

What about the logarithmic option in the Spectrograph~ object's option  
dialog isn't working for you?  What else do you need it to do?

If you have Jitter, you can look at jit-examples/audio/audio-viz/ 

1.audioviz_simple_jit_fft.pat. This should do what you need. The 

log display works by generating a power function in a buffer~ which 

is used by lookup~ to warp the x axis of the graph.

If you have Jitter, you can look at jit-examples/audio/audio-viz/ 
1.audioviz_simple_jit_fft.pat.  This should do what you need.  The  
log display works by generating a power function in a buffer~ which  
is used by lookup~ to warp the x axis of the graph.

Thanks, this approach is working for me now!

i needed a bipolar graph of the difference between two spectra.

log frequency graphing