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

have fun, jim

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?

_Mark

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.

-Randy

Thanks, this approach is working for me now!

-Alex

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

-Alex