Monthly Archives: April 2013

Song 10 – Strange Death

I’ve not posted any music in quite a while so here’s the 10th song/demo that I was working late last year (the others can be heard here). I never got round to recording the vocals to it and had a bit of free time a few weekends ago so I thought I might as well do it while I had the time.

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Optimised Stereo

Our ears use different methods of hearing at different frequencies to allow us to localise sound. We use phase differences at low frequencies and level/intensity differences at high frequency (a slight simplification but it’ll do). Traditional amplitude panning actually recreates these low frequency cues if you’re sitting in the sweet spot i.e. equidistant from both loudspeakers.

But there’s a problem: using the same amplitude across the whole frequency spectrum means that the cues for the low frequency tell your brain that the image is one one direction and the high frequency cues tell it that it’s in another direction.

Perceived localised image position from Gerzon's Velocity and Energy vectors

Perceived localised image position from Gerzon’s Velocity and Energy vectors for standard amplitude panning

A very smart man (which is underselling him) called Michael Gerzon developed two vectors, known as the Velocity and Energy vectors, that can give you an idea of where a sound will be perceived if you know the loudspeaker gains. The Velocity vector is an indication for low frequencies below approximately 700 Hz and Energy vector for high frequencies. If we consider the prediction a standard stereo set-up (2 loudspeakers and a listener forming an equilateral triangle) shown to the right then there is indeed a discrepancy between the directions of the two Gerzon vectors!

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The Joys of Varispeed

Varispeed (changing the speed and pitch of audio like you could do with tape) is one of my favourite audio effects. It was more common in the analogue days because it was easier to slow tapes down that to do the equivalent with digital. [Cockos’ Reaper has a great varispeed facility but several DAWs (Sonar, I’m looking at you…) have yet to implement anything like it. This is actually one of the main reasons I’ve started to migrate from Sonar to Reaper.] Varispeed is the thing that lets you get the “Chipmunk” vocals.

But sounding like The Chipmunks isn’t why it’s interesting – that’s even to be avoided! Nor am I talking about slowing tape down to half speed, playing and guitar solo and pretending you’re Eddie Van Halen. That’s one possible use but is rather crude. No, it’s about getting new and interesting sounds out of the same instruments.

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