SoundHack is an excellent little bit of free software for Mac. Its time and pitch stretching effects are actually far better than the standard Digidesign plug-ins for Pro Tools, they’re just a little less intuitive to use.
Before we get stuck in, a couple of things to note:
Right then, first open up SoundHack, then click file > open and choose the audio file that you want to play with. I’ll use a little clip of some double tracked guitar. Before any SoundHacking commences, it sounds like this:
You’ll notice this window pop up, which represents the sound file.
How an audio file is represented in SoundHack
Now click Hack and the list of audio-mangling tools at your disposal will appear.
Phase Vocoder
I’ll start with the Phase Vocoder (because it’s my favourite). This is the tool that does all the pitch and time manipulation. You can change the pitch or speed of a bit of audio by a set amount, or vary it over time using the edit function. Here’s what it looks like:
SoundHack Phase Vocoder
There are various parameters here relating to what’s known as a Fast Fourier Transform, which is the computational method of pitch shift and time stretch. Unless you really want to get into the technical side of the process, I’d leave them be for now. Instead click the edit function, and here is a function of pitch over time. I drew in the following line:
The edit function in the Phase Vocoder
Then click done, and then process. It may take a little time to process, but when it’s done another window representing your new sound file pops up. That bit of guitar with that pitch shift function applied sounds like this:
If you want the whole thing just to be changed by a particular amound, deselect the button next to “scaling function” and enter a value in the box that appears above the pitch scale button. This can be applied to time stretching in the same way, just be selecting time scale rather than pitch scale.
Convolution
The convolution tool basically multiplies one audio sample by another, similar to ho a ring modulator convolutes a sound source with a sine wave. If we take our guitar audio and click the “choose impulse” button and then use a drum beat as the impulse, the result is this:
Er, well, it’s different to say the least. Let’s try using some pitched material as the impulse, a bit of acoustic guitar for example.
It takes some experimenting, clearly, but you get the idea!
Mutation
Mutation works in a similar manor to convolution. However instead of multiplying to audio sources together it uses one to mutate another. So if we pick our guitar track and choose the drum track as a target, this is the result:
Varispeed
Similar to the phase vocoder, this uses a function to alter the speed and pitch of a sound source over time. It is different from the vocoder because it varies the speed and pitch together, rather than separately. Here’s an example:
In conclusion…
This a great little bit of software, especially seeing as it’s free. How you can work in some of the weird and wonderful sounds into your own music is a different matter. It’s good to have the capability to make odd noises at your disposal though!
I’ll be looking into other ways to make “weird” noises soon. If you have any questions feel free to comment.
Graeme Allen is the MD at Amati Studios, the nation-wide recording studio company.
