Binaural Sound and IRs

Filtering occurs through the addition of time shifted reflections

All these filters are direction dependent (except for the ear canal)

These effects are called HRTF (Head related transfer function)

If you think of all these elements as a single linear system, the HRTF perfectly represents it and its effect on any incoming signal

But of course sound arriving from a different direction will cause the system to behave differently, so there are in fact as many HRTFs as there are possible source positions

Linear time-invariant systems can be perfectly represented by their impulse response

Impulse response: pass the shortest impulse posible through the system and capture the effect of the system on it

Although in practice rather than using impulses, sine sweeps, MLS or Golay codes are used as they exhibit better signal to noise ratio.

impulses are broadband

so they capture the effect of the system for all frequencies

Room Impulse Responses

Convolution

Impulse responses for an HRTF system are called HRIRs (Head-related impulse responses)

There are several HRIR sets available on the net

Some are recorded with dummy head microphones, other use human subjects with in-ear microphones

The HRIR set conatins many two channel files, one for each measured direction

Since the HRIRs represent discrete points in space, movement must be simulated through some form of interpolation or approximation

Issues with HRTF binuaral rendering

Binaural Room IRs

Directional Room IRs

Publicly available databases

Formats

Virtual reality/Virtual environments

Headphone reproduction

BRIRs can be used to prototype sounds for particular venues

Binaural sound and recording