I was recently trying to create a sine wave frequency sweep audio sample file to test out a digital signal processing (DSP) filter I was trying to write. Using Audacity, you can create plug-ins to achieve all sorts of cool effects. After a little experimentation I came up with the following code:
;nyquist plug-in ;version 1 ;type generate ;name "Frequency Sweep" ;action "Producing frequency sweep..." ;info "by Adam Pope" ;control startf "Start Frequency (Hz)" real "" 1 0 20000 ;control endf "End Frequency (Hz)" real "" 10000 0 30000 ;control duration "Duration (secs)" real "" 20 1 300 ;control type "Sweep scale [1=Linear, 2=Exponential]" int "" 1 1 2 ;control other "I dont know what this does" real "" 5 0 100 (if (= type 2) (fmosc startf (pwe duration endf other)) (fmosc startf (pwl duration endf other)) )
Copy this code into a frequencysweep.ny file and place it in your Audacity plug-ins directory. You’ll need to restart audactity for it to register the new plug-in. Once you’re back in, click on ‘Generate’ on the menu bar and select ‘Frequency Sweep’ from the list of options. You will then be presented with a dialog containing sliders to play with the parameters of your sweep. If any of the limits are too restricitve for you, simply change the values in the plug-in file!
If anybody can explain what the 3rd parameter of pwe and pwl does, I’d love to know!
Update: Many thanks to Paul Schimmel who sent me this updated version which removes the unknown parameter and also adds output level control.
;nyquist plug-in ;version 1 ;type generate ;name "Frequency Sweep..." ;action "Producing frequency sweep..." ;info "by Adam Pope and Paul Schimmel" ;control startf "Start Frequency (Hz)" real "" 20 20 20000 ;control endf "End Frequency (Hz)" real "" 20000 20 20000 ;control duration "Duration (secs)" real "" 30 1 300 ;control level "Level (dBFS)" real " " 0 -40 0 ;control type "Sweep scale [1=Linear, 2=Exponential]" int "" 2 1 2 (if (= type 2) (scale-db level (fmosc 0 (pwev startf duration endf))) (scale-db level (fmosc 0 (pwlv startf duration endf))) )
