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Usage of impulse responses

As described in :ref:`the general usage of the database <sec-database-usage>` there are several ways to get the data downloaded to your PC.

Usage of |HRTF|s

Let us now assume that you want to have a cello sound convolved with an |HRTF| in order to perceive it from the right side:

sigfile = xml.dbGetFile('stimuli/anechoic/instruments/anechoic_cello.wav');
sig = wavread(sigfile);
hrtffile = xml.dbGetFile('impulse_responses/qu_kemar_anechoic/QU_KEMAR_anechoic_3m.sofa');
% Load your impulse response into a struct
hrtf = SOFAload(hrtffile);
% Display some information about the impulse response
SOFAinfo(hrtf);
% Plot a figure with the measurement setup
SOFAplotGeometry(hrtf);
% Have a look at the size of the data
size(hrtf.Data.IR)
% Get information about the measurement setup
hrtf.ListenerPosition       % position of dummy head
hrtf.SourcePosition         % position of loudspeaker
% Head orientation of the dummy head + coordinate system and units
hrtf.ListenerView
hrtf.ListenerView_Type
hrtf.ListenerView_Units
% Calculate the source position from a listener point of view
apparentSourceVector = SOFAcalculateAPV(hrtf);
% Listen to the HRTF with azimuth of -90°
apparentSourceVector(91, 1)
SOFAplotGeometry(hrtf, 91);
soundOutput = [conv(squeeze(hrtf.Data.IR(91, 1, :)), sig) ...
               conv(squeeze(hrtf.Data.IR(91, 2, :)), sig)];
sound(soundOutput, hrtf.Data.SamplingRate);

You could do the same by not using the SOFA API directly, but by using only functions from the |BinSim|:

% Load HRTF data set
hrtf = simulator.DirectionalIR( ...
    xml.dbGetFile('impulse_responses/qu_kemar_anechoic/QU_KEMAR_anechoic_3m.sofa'));
% Get a the HRTF for an azimuth of 80° (this is to the left of you)
impulseResponse = hrtf.getImpulseResponses(80);
figure;
plot(impulseResponse.left(1:400), '-b');
hold on;
plot(impulseResponse.right(1:400), '-r');
% Listen to the output signal
outputSignal = [conv(impulseResponse.left, sig) ...
                conv(impulseResponse.right, sig)];
sound(outputSignal, hrtf.SampleRate);

Usage of |BRIR|s

The following will use |BRIR|s measured by the :ref:`Two!Ears KEMAR in the Adream building <sec-brir-twoears-adream>`. They contain several listening positions and loudspeakers.

Fix listener with head movements

We first start with a measurement done at one position including several head orientations and four different loudspeakers.

To get more information about the data in Matlab, you can try the following. Note also, that all angles are specified in world coordinates, where 0° is always located parallel to the x-axis.

>> hrtf = SOFAload('TWOEARS_KEMAR_ADREAM_pos1.sofa', 'nodata');
>> % Get 0° look direction of listener
>> SOFAconvertCoordinates(hrtf.ListenerView(40,:), ...
                          hrtf.ListenerView_Type, 'spherical')

ans =

 -105.7541         0    1.0000

>> % Get min and max head orientation
>> SOFAconvertCoordinates(hrtf.ListenerView(1,:), ...
    hrtf.ListenerView_Type, 'spherical')

ans =

  176.2459         0    1.0000

>> SOFAconvertCoordinates(hrtf.ListenerView(end,:), ...
    hrtf.ListenerView_Type, 'spherical')

ans =

  -27.7541         0    1.0000

>> % Get loudspeaker position
>> hrtf.EmitterPosition

ans =

    2.5500    7.4700    1.0200
   -3.6600    7.1500    1.0900
   -3.3000    5.0900    1.0800
   -1.4400    2.9800    0.3100

>> % Get relative direction of second loudspeaker from listeners' view
>> loudspeakerDirection = SOFAconvertCoordinates( ...
    hrtf.EmitterPosition(2,:)-hrtf.ListenerPosition, ...
    'cartesian', 'spherical');
>> listenerView = SOFAconvertCoordinates(hrtf.ListenerView(40,:), ...
    hrtf.ListenerView_Type, 'spherical');
>> loudspeakerDirection - listenerView

ans =

  -50.5197   -3.1852    5.8391

Moving listener without head rotations

The second part of the measurement consists of a trajectory of 20 listener positions at which |BRIR|s were measured. This measurement includes only a fixed head orientation of 0°, but the same 4 loudspeaker positions as the first one.

Again, to get more information about the data in Matlab, you can try the following. Note also, that all angles are specified in world coordinates, where 0° is always located parallel to the x-axis.

>> hrtf = SOFAload('TWOEARS_KEMAR_ADREAM_trajectory.sofa', 'nodata');
>> % Get number of listener positions
>> size(hrtf.ListenerPosition, 1)

ans =

    20

>> % Plot the trajectory
>> figure; plot(hrtf.ListenerPosition(:,1), hrtf.ListenerPosition(:,2), 'x')
>> axis square
>> axis([-5.25 4.25 -1 11.25])
>> % Get the direction of the third loudspeaker from a listeners' view
>> loudspeakerDirection = SOFAconvertCoordinates( ...
    repmat(hrtf.EmitterPosition(3,:),[20 1])-hrtf.ListenerPosition, ...
    'cartesian', 'spherical');
>> listenerView = SOFAconvertCoordinates(hrtf.ListenerView, ...
    hrtf.ListenerView_Type, 'spherical');
>> wrapTo180(loudspeakerDirection - listenerView)

    ans =

      -37.2047   -3.2396    6.4321
      -37.7142   -3.2855    6.3284
      -39.4842   -3.4401    5.9994
      -41.9584   -3.7243    5.5815
      -43.7411   -3.8833    5.3198
      -45.1726   -4.0115    5.1267
      -46.7272   -4.1598    4.9251
      -48.5749   -4.3518    4.7064
      -50.6048   -4.5234    4.4802
      -52.7507   -4.7302    4.2677
      -54.6393   -4.8501    4.1118
      -57.2112   -5.0477    3.9111
      -59.6051   -5.2142    3.7414
      -62.2329   -5.4230    3.5689
      -65.6560   -5.7044    3.3784
      -68.7011   -5.9200    3.2496
      -87.0739   -6.1044    3.1724
      -96.2958   -6.0686    3.2225
     -105.3502   -5.8268    3.3804
     -109.6098   -5.7063    3.4695