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Streaming audio on the digital to analog converter

This demo is exactly the same as Generating audio with the digital to analog converter, except that it streams the audio instead of loading it all at once. You can refer to the previous demo for more information.

function DatapixxDacWaveStreamDemo(wavFilename)
% DatapixxDacWaveStreamDemo([wavFilename=funk.wav])
% Demonstrates how to continuously stream an audio waveform to the DATAPixx DAC
% (Digital to Analog Converter) subsystem.
% The precision DACs are capable of updating at up to 1 MHz, and can be used to
% generate arbitrary analog waveforms with an output swing of up to +-10V.
% One application of the DACs is for the generation of precise audio stimuli.
% The audio CODECs found in typical consumer electronics have serial interfaces.
% Internally, the CODEC processes the serial data with digital interpolation
% filters, a delta-sigma modulator, and an analog reconstruction filter.
% One result is that a single dataset played back on two different CODECs
% can result in slightly different analog waveforms. Using DACs eliminates this
% variation.
% A second issue is the CODEC group delay. CODECs introduce a delay between
% when they receive their serial data, and when their analog outputs update.
% This delay varies from one CODEC to another, and also varies within a single
% CODEC depending on waveform update rate. Using DACs eliminates this variation.
% Note that the DAC outputs are not intended to drive very heavy loads. It is
% possible to drive up to +-1V waveforms (like those used in PsychPortAudio)
% directly into 32 Ohm headphones, or up to +-10V waveforms into high impedance
% (eg: 400 Ohm) headphones like those used for studio quality sound. For higher
% power, or for driving 8 Ohm speaker loads, add an external headphone amplifier.
% Optional argument:
% wavFilename = Name of a .wav sound file to load and play.
%               Otherwise the funk.wav provided with PsychToolbox is used.
% Also see: DatapixxDacWaveDemo
% History:
% Oct 1, 2009  paa     Written
% Oct 29, 2014 dml     Revised 

AssertOpenGL;   % We use PTB-3

% Get the .wav filename
if nargin < 1
    wavFilename = [];
if isempty(wavFilename)
    wavFilename = [PsychtoolboxRoot 'PsychDemos' filesep 'SoundFiles' filesep 'funk.wav'];

% Load the .wav file
[waveData, freq] = audioread(wavFilename);
waveData = waveData';               % Transpose so that each row has 1 channel
nChannels = size(waveData, 1);
nTotalFrames = size(waveData, 2);

% We'll demonstrate streaming with a 1 second buffer,
% and update the streaming buffer no faster than 100 times per second.
nBufferFrames = freq;
if (nBufferFrames > nTotalFrames)
    nBufferFrames = nTotalFrames;
minStreamFrames = floor(freq / 100);

% Open Datapixx, and stop any schedules which might already be running
Datapixx('RegWrRd');    % Synchronize DATAPixx registers to local register cache

% Fill the buffer with as much of the data that fits.
% First write to DAC buffer must be in non-streaming mode.
Datapixx('WriteDacBuffer', waveData(:,1:nBufferFrames));

% Configure the DATAPixx to play the buffer at the correct frequency.
% If the .wav file has a single channel, it will play on DAC channel 0.
% Additional .wav channels will play on increasing DAC channel numbers. 
Datapixx('SetDacSchedule', 0, freq, nTotalFrames, [0: nChannels-1], 0, nBufferFrames);

% Start the playback
Datapixx('RegWrRd');    % Synchronize DATAPixx registers to local register cache

% Continuously feed the streaming buffer until the entire waveform has been played,
% or until a key is pressed.
fprintf('\nWaveform playback starting, press any key to abort.\n');
if (exist('OCTAVE_VERSION'))
nextWriteFrame = nBufferFrames + 1;
nFramesLeft = nTotalFrames - nBufferFrames;
while nFramesLeft > 0
    Datapixx('RegWrRd');   % Update registers for GetDacStatus
    status = Datapixx('GetDacStatus');
    if status.freeBufferFrames >= minStreamFrames           % Do not waste CPU time doing millions of tiny buffer updates
        if status.freeBufferFrames >= nFramesLeft           % Stream buffer has room for remainder of the waveform?
            nStreamFrames = nFramesLeft;                    % This iteration will download the remainder of the waveform
            nStreamFrames = status.freeBufferFrames;        % Top off stream buffer with a section of waveform
        Datapixx('WriteDacBuffer', waveData(:, nextWriteFrame: nextWriteFrame+nStreamFrames-1), -1);    % Download waveData
        nextWriteFrame = nextWriteFrame + nStreamFrames;    % Update for next iteration
        nFramesLeft = nFramesLeft - nStreamFrames;

    % A keypress will immediately abort the schedule
    if (KbCheck)
        Datapixx('RegWrRd');    % Synchronize DATAPixx registers to local register cache

% Show final status of DAC scheduler
fprintf('\nStatus information for DAC scheduler:\n');
Datapixx('RegWrRd');   % Update registers for GetDacStatus

% Job done
fprintf('\nDemo completed\n\n');
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