I have taken my HRTF routine and used it to record my first test impulse responses. This is essentially the same method for capturing HRTFs, except it was done with a single omnidirectional microphone placed in the speaker array (instead of a person).
I set the equipment up to play the full 50-channel sweeps, however only two sets of five sweeps, back-to-back and overlapped, were needed, and so recorded, for this test. In both cases five sweeps play out of separate speakers at different times, the only difference being that in the overlapped method, the sweeps are playing at the same time (actually staggered by half a second).
After processing the sweeps in MATLAB, I was left with two sets of five impulse responses, two of which I have pictured below. The two IRs are taken from different recordings of the same speaker.
If you looked and thought “thats the same image in both boxes” then clearly this was a success. Running them through MATLAB’s ‘corrcoef’ function they came out 99.78% correlated, which could be further improved by either driving the speakers harder (improve signal-noise-ratio), or lengthening the sweeps from five seconds to ten.
So moving on from here my next job is to take an actual set of HRTFs, which is basically repeating today’s work, with more stuff.
(The main equipment used was: Reaper (a DAW that excels at multi-input/output routing) to route each channel of a 50-channel .wav file to an independent speaker, an Earthworks M30 measurement microphone, which features an exceptionally flat frequency response and a Sound Devices MixPre-D preamp. Also a 50-Genelic-speaker-array).