Documentation

dsp.AudioPlayer System object

Package: dsp

Play audio data using computer's audio device

Description

The AudioPlayer object plays audio data using the computer's audio device.

To play audio data using the computer's audio device:

  1. Define and set up your audio player object. See Construction.

  2. Call step to play audio data according to the properties of dsp.AudioPlayer. The behavior of step is specific to each object in the toolbox.

This System object™ buffers the data from the audio device using the process illustrated by the following figure.

Construction

H = dsp.AudioPlayer returns an audio player object, H, that plays audio samples using an audio output device in real-time.

H = dsp.AudioPlayer('PropertyName',PropertyValue, ...) returns an audio player object, H, with each property set to the specified value.

H = dsp.AudioPlayer(SAMPLERATE,'PropertyName',PropertyValue, ...) returns an audio player object, H, with the SampleRate property set to SAMPLERATE and other specified properties set to the specified values. This System object supports variable-size input. If you use variable-size signals with this System object, you may experience sound dropouts when the size of the input frame increases. To avoid this behavior, use a signal of maximum expected size when you first call step to start running through this System object.

Properties

DeviceName

Device to which to send audio data

Specify the device to which to send the audio data. The default is Default, which is the computer's standard output device. You can use tab completion to query valid DeviceName assignments for your computer by typing H.DeviceName = ' and then pressing the tab key.

SampleRate

Number of samples per second sent to audio device

Specify the number of samples per second in the signal as an integer. The default is 44100. This property is tunable.

DeviceDataType

Data type used by device

Specify the data type used by the audio device to acquire audio data as Determine from input data type , 8-bit integer, 16-bit integer, 24-bit integer, or 32-bit float. The default is Determine from input data type.

BufferSizeSource

Source of Buffer Size

Specify how to determine the buffer size as Auto or Property. The default is Auto. When this property is set to Auto, an appropriate buffer size based on the SampleRate gets computed.

BufferSize

Buffer size

Specify the size of the buffer that the audio player object uses to communicate with the audio device as an integer. BufferSize is half the size of the sound card buffer. A frame of data cannot be passed to the queue until the device empties the buffer, which introduces latency. Latency is the time it takes the device to empty the queue and the buffer. BufferSize has to be smaller than the effective queue duration. This property is tunable. Tuning this property involves a balance between device latency and the possibility of dropping data (buffer underrun).

This property applies when you set the BufferSizeSource property to Property. The default is 4096. To set the BufferSize to a value other than the default, first change the BufferSizeSource to 'Property'. You can select BufferSize in the list of properties.

QueueDuration

Size of queue in seconds

Specify the length of the audio queue, in seconds. The default is 1.0. This property is tunable. The purpose of the queue is to control the trade-off between latency and data dropout. Latency is calculated by the following equation: latency=QueueDuration×SampleRate+2×BufferSizeSampleRate.

To minimize latency, lower the QueueDuration or set it to 0. However, be aware that data dropouts or loss of system robustness may result. The Queue duration property specifies the duration of the signal, in seconds, that can be buffered during the simulation. This value is the maximum length of time that the System object's data supply can lag the device's data demand. If the MATLAB® data throughput rate is lower than the device throughput rate, a buffer underrun occurs. You can use OutputNumUnderrunSamples to monitor underrun. To correct the underrun, make the queue duration larger than the buffer. If the MATLAB data throughput rate is higher than the device throughput rate, a buffer overrun occurs, causing the System object to wait before writing data to the queue. To minimize the chance of dropouts, the System object checks to verify the queue duration is at least as large as the maximum of the buffer size and the frame size. If it is not, the queue duration is automatically set to this maximum value. At the start of the simulation, the queue is filled with silence. At each time step, the System object sends a buffer of samples from the top of the queue to the audio device. If the queue does not contain enough data to completely fill the buffer, the System object fills the remaining portion of the buffer with zeros.

OutputNumUnderrunSamples

Enable output of underrun count

Set to true to output the number of zero samples inserted due to queue underrun since the last call to the step method. The default is false.

ChannelMappingSource

Source of device channel mapping

Specify whether to determine the channel mapping as 'Auto' or as 'Property'. If you set the value of ChannelMappingSource to 'Auto', the ChannelMapping field is rendered inactive. If you set this property to 'Property', the vector specified in the ChannelMapping field is used to route the output.

ChannelMapping

Data-to-device channel mapping

Vector of valid channel indices to represent the mapping between data and device output channels. The term Channel Mapping refer to a 1-to-1 mapping that associates channels on the selected audio device to channels of the data. When you play audio, channel mapping allows you to specify which channel of the audio data to output a specific channel of audio data. By default, the ChannelMapping field is [1:MAXOUTPUTCHANNELS], where MAXOUTPUTCHANNELS depends upon the selected device.

Methods

cloneCreate audio player object with same property values
getNumInputsNumber of expected inputs to step method
getNumOutputsNumber of outputs of step method
isLockedLocked status for input attributes and nontunable properties
releaseAllow property value and input characteristics changes
stepWrite audio to audio output device

Examples

Read in an AVI audio file, and play the file back using the standard audio output device:

AFR = dsp.AudioFileReader; % points to a default audio file
AP = dsp.AudioPlayer('SampleRate',AFR.SampleRate, ...
			'QueueDuration',2, ...
			'OutputNumUnderrunSamples',true);
while ~isDone(AFR)
  audio = step(AFR);
  nUnderrun = step(AP,audio);
  if nUnderrun > 0
    fprintf('Audio player queue underrun by %d samples.\n'...
	     ,nUnderrun);
  end
end
pause(AP.QueueDuration); % wait until audio is played to the end
release(AFR);            % close the input file
release(AP);             % close the audio output device

To learn how to measure and tune audio throughput using this object, see the Measuring Audio Latency example.

Troubleshooting

Running an Executable Outside MATLAB

To run your generated standalone executable application in Shell, you need to set your environment to the following:

PlatformCommand
Macsetenv DYLD_LIBRARY_PATH $LD_LIBRARY_PATH: $MATLABROOT/bin/maci64 (csh/tcsh)

export DYLD_LIBRARY_PATH $LD_LIBRARY_PATH: $MATLABROOT/bin/maci64 (Bash)

Linuxsetenv LD_LIBRARY_PATH $LD_LIBRARY_PATH: $MATLABROOT/bin/glnxa64 (csh/tcsh)

export LD_LIBRARY_PATH $LD_LIBRARY_PATH: $MATLABROOT/bin/glnxa64 (Bash)

Windowsset PATH = $MATLABROOT\bin\win32;%PATH%

set PATH = $MATLABROOT\bin\win64;%PATH%

Algorithms

This object implements the algorithm, inputs, and outputs described on the To Audio Device block reference page. The object properties correspond to the block parameters.

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