SoundHack is a free audio processing application with a great deal of power, if you can get past the ’90s interface and non-standard menu commands. SoundHack performs a single audio process (at a time) on a whole file. As such, it lacks a graphic waveform view, but does allow for function drawing in a somewhat clunky window for certain processes.
Varispeed
For now, we’ll use the Varispeed (cmd-V) process to alter playback speed and pitch dependently. You can adjust playback speed in Audacity and Peak, but SoundHack lets you draw speed change functions, allowing for infinite variations of glissandi.
Open a sound file (if you have more than one open, make sure the one you want to process is the active window), and then choose the Varispeed command from the Hack menu. A window will open that looks like this:
Make sure to set the Quality to “Best.” I typically choose “Vary by Pitch” rather than by scale, but either can be used. Check Varispeed, and then click on the “Varispeed Function” button. That brings up the this window:
The horizontal line represents the pitch shift in semitones throughout the file. The default opening is no pitch change. The top right box shows the max increase in pitch change possible; the lower right box shows the maximum pitch decrease possible (mine doesn’t show a number, but it is usually -60). If you want to shift the entire file by a single pitch change amount, use the Set button and type in a value. If you want a change over time, use the mouse and slowly draw in the function area.
Before drawing, I usually change the Top and Bottom ranges to something that zooms in to my desired change range. Here I’ve set the values to +12 and -24.
Drawing takes both care and patience. The drawing function doesn’t like fast mouse movements, and it tends to not recognize drawing at the left and right edges of the box. I will slowly go back and forth at the edges to get close to the function I want. After drawing, it is usually helpful to use the Smooth button (repeatedly) to get rid of sharp edges on the function, which usually are artifacts of the drawing process. Here is a function that I drew that starts at 0, moves up to around +10, and then back down to close to -24.
Notice that the Semitones readout in the lower right shows you how much you are shifting the pitch as you draw. One you have a function you like, click Done.
Now you’re back in the first Varispeed window. Click Process, which brings up a save dialog box for naming the file. SoundHack does NOT add file extensions to your file. You have to type those in. You also need to delete the old extension name, which has been conflated into the file name. Pick a meaningful file name and add a “.aiff” extension. Note: SoundHack does not allow for long filenames. When you have gone over the allowed name length, the save button will gray out.
Once you save the file, a new window will open and contain the output of your process. You can play the new file with the spacebar.
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