hrtfmove2
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## hrtfmove2

hrtfmove2 — Generates dynamic 3d binaural audio for headphones using a Woodworth based spherical head model with improved low frequency phase accuracy.

## Description

This opcode takes a source signal and spatialises it in the 3 dimensional space around a listener using head related transfer function (HRTF) based filters.

## Syntax

    aleft, aright hrtfmove2 asrc, kAz, kElev, ifilel, ifiler [,ioverlap, iradius, isr]

## Initialization

ifilel -- left HRTF spectral data file

ifiler -- right HRTF spectral data file

| Note
Spectral datafiles (based on the MIT HRTF database) are available in 3 different sampling rates: 44.1, 48 and 96 khz and are labelled accordingly. Input and processing sr should match datafile sr. Files should be in the current directory or the SADIR (see Environment Variables).

| Note
HRTF Data files for use with hrtfmove, hrtfmove2, hrtfstat, hrtfearly, hrtfreverb were updated for Csound 5.15 and later (the code was updated and is more efficient). Old datafiles are now deprecated.

ioverlap -- optional, number of overlaps for STFT processing (default 4). See STFT section of manual.

iradius -- optional, head radius used for phase spectra calculation in centimeters (default 9.0)

isr - optional, default 44.1kHz, legal values: 44100, 48000 and 96000.

## Performance

asrc -- Input/source signal.

kAz -- azimuth value in degrees. Positive values represent position on the right, negative values are positions on the left.

kElev -- elevation value in degrees. Positive values represent position above horizontal, negative values are positions below horizontal (min -40).

Artifact-free user-defined trajectories are made possible using an interpolation algorithm based on spectral magnitude interpolation and a derived phase spectrum based on the Woodworth spherical head model. Accuracy is increased for the data set provided by extracting and applying a frequency dependent scaling factor to the phase spectra, leading to a more precise low frequency interaural time difference. Users can control head radius for the phase derivation, allowing a crude level of individualisation. The dynamic source version of the opcode uses a Short Time Fourier Transform algorithm to avoid artefacts caused by derived phase spectra changes. STFT processing means this opcode is more computationally intensive than hrtfmove using phase truncation, but phase is constantly updated by hrtfmove2.

## Examples

Here is an example of the hrtfmove2 opcode. It uses the file hrtfmove2.csd.

Example 446. Example of the htrfmove2 opcode.

    <CsoundSynthesizer>
    <CsOptions>
    ; Select flags here
    ; realtime audio out
     -o dac
    ; For Non-realtime ouput leave only the line below:
    ; -o hrtf.wav
    </CsOptions>
    <CsInstruments>

    sr = 44100
    kr = 4410
    ksmps = 10
    nchnls = 2

    gasrc init 0

    instr 1		;a plucked string

      kamp = p4
      kcps = cpspch(p5)
      icps = cpspch(p5)

      a1 pluck kamp, kcps, icps, 0, 1

      gasrc = a1

    endin

    instr 10	;uses output from instr1 as source

     kaz	linseg 0, p3, 720		;2 full rotations

     aleft,aright hrtfmove2 gasrc, kaz,0, "hrtf-44100-left.dat","hrtf-44100-right.dat"

     outs	aleft, aright

    endin

    </CsInstruments>
    <CsScore>

    ; Play Instrument 1: a simple arpeggio
    i1 0 .2 15000 8.00
    i1 + .2 15000 8.04
    i1 + .2 15000 8.07
    i1 + .2 15000 8.11
    i1 + .2 15000 9.02
    i1 + 1.5 15000 8.11
    i1 + 1.5 15000 8.07
    i1 + 1.5 15000 8.04
    i1 + 1.5 15000 8.00
    i1 + 1.5 15000 7.09
    i1 + 1.5 15000 8.00

    ; Play Instrument 10 for 10 seconds.
    i10 0 10

    </CsScore>
    </CsoundSynthesizer>

## See also

Panning and Spatialization: Binaural spatialization

More information on this opcode: http://www.csoundjournal.com/issue9/newHRTFOpcodes.html, written by Brian Carty

## Credits

Author: Brian Carty
Maynooth
2008

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