AudioPlayer Serial Interface

Description

Allows the state machine or PC to play mono or stereo sounds using Ch1 + Ch2 of the analog output module.

Requires a 4-channel analog output module board with BpodAudioPlayer or BpodAudioPlayerLive firmware loaded from:

• https://github.com/sanworks/Bpod_AnalogOutput_Firmware/tree/master/AnalogOutputModule_4ch
  • Note: The 'Live' version of BpodAudioPlayer allows sounds to be loaded while playback is in progress, but is limited to 44.1kHz sampling. The analog output module must be connected to a module port on the state machine.

NOTE: the Analog Output Module is not a sound card! If you need high quality audio playback, use the Bpod HiFi module.

State Machine Command Interface

The state machine command interface consists of bytes sent from the Bpod state machine to the AudioPlayer module to start and stop playback.

• Byte 255 (reserved): Returns module info to state machine
• 'P' (ASCII 80): Plays a sound.
  • 'P' (byte 0) must be followed by one byte:
    • Byte 1: The sound to play (zero-indexed).
• 'X' (ASCII 88): Stop all playback
• 'x' (ASCII 120): Stop playing a specific sound (if that sound happens to be playing)
  • 'x' (byte 0) must be followed by one byte:
    • Byte 1: The sound to stop (zero-indexed).

SerialUSB Command Interface

The SerialUSB command interface allows configuration of the AudioPlayer module from MATLAB or Python before a trial begins. The AudioPlayer class for Bpod/MATLAB wraps this interface. The first two commands are the same as for the state machine interface, and additional commands follow.

• (ASCII 229): Handshake and reset. The module replies with the following sequence of bytes:
  • handshakeReply (1 byte); Equal to 230
  • firmwareVersion(4 bytes; 32-bit int); the current firmware version
  • Note: This op will cancel any currently playing or loading sounds, reset the sampling rate to default 44.1kHz, and clear any previously loaded sounds.
• 'L' (ASCII 76): Load an audio waveform. 'L' (byte 0) is followed by:
  • Byte 1: The waveform to load (0-19). Note: In the AudioPlayer plugin, these are corrected for MATLAB's indexing (1-20).
  • Byte 2: isStereo (set to 1 if loading a stereo/2ch waveform, or 0 if mono/1ch). Note: Both speakers play mono waveforms.
  • Bytes 3 - 6: The number of samples in the audio waveform expressed as a 32-bit integer (1-1,000,000).
  • Bytes 7 - (7+((2 + (2*isStereo))*nSamples)): The waveform. Each byte is a 16-bit integer coding for a voltage in the range -5 to +5.
  • The AudioPlayer module returns a byte (1) to confirm that it has finished reading the last sample.
• '>' (ASCII 76): Load an audio waveform in safe mode (slower than 'L'). '>' (byte 0) is followed by bytes as described in op 'L' above.
  • The AudioPlayer module returns a byte (1) to confirm that it has finished reading the last sample.
• 'S' (ASCII 83): Set sampling period (units = microseconds, default = 22.675737; sampling rate = 44.1kHz). 'S' (byte 0) is followed by:
  • Bytes 1-4: Sampling period in microseconds (32-bit float)
  • The AudioPlayer class (MATLAB) exposes sampling rate to the user, and computes sampling period before transmitting.
  • The AudioPlayer module returns a byte (1) to confirm that it has finished setting the sampling period. -'*' (ASCII 42): Push any loaded sounds to current playback buffers*.
  • Note: This op will make any sounds loaded recently current at the loaded positions, replacing any sounds at those positions.
    • Thus, if new sounds for positions 2 and 3 are loaded during a trial for use on the next trial, sending '*' will make these waveforms the current sounds at positions 2 and 3.
  • The AudioPlayer module returns a byte (1) to confirm that it has finished pushing loaded sounds.
• 'E' (ASCII 69): Enable AM envelope. 'E' (byte 0) is followed by:
  • Byte 1: UseAMEnvelope: 1 if using AM envelope, 0 if not.
  • The AudioPlayer module returns a byte (1) to confirm that it has finished setting the loop mode.
• 'M' (ASCII 77): Load AM envelope. 'M' (byte 0) is followed by:
  • Bytes 1-2: EnvelopeSize (16-bit unsigned int): The number of samples in the envelope
  • Bytes 3-(3+EnvelopeSize*4): samples of the 16-bit AM envelope. These are 4-byte floats (attenuating factors) in range [0 to 1].
  • The AudioPlayer module returns a byte (1) to confirm that it has finished storing the AM envelope. -'Y' (ASCII 89): Setup MicroSD card*.
  • Note: This op must be run before use with a new microSD card. It may take up to 1 minute to complete.
  • The AudioPlayer module returns a byte (1) to confirm that it has finished setting up the microSD card.
• 'O' (ASCII 79): Set loop mode for a waveform. 'O' (byte 0) is followed by:
  • Bytes 1-20: Loop mode bytes. Each byte represents a waveform: 1 if using loop mode, 0 if not.
  • The AudioPlayer module returns a byte (1) to confirm that it has finished setting the loop mode. -'-' (ASCII 45): Set duration for looping playback on a single trigger.* '-' (byte 0) is followed by:
  • Bytes 1-21: Duration of looped playback on trigger for each waveform (expressed in samples) as a 32-bit integer.
    • Note: Because loop duration is expressed in samples, it must be re-loaded following sampling rate changes (see op above, 'S')
  • The AudioPlayer module returns a byte (1) to confirm that it has finished setting the loop duration.
• 'V' (ASCII 86): Set start/stop event reporting to the state machine. 'V' (byte 0) is followed by:
  • Byte 1: 1 to report waveform on and off events, 0 if not.
  • Note: start and stop events are returned as bytes to indicate each waveform's playback start OR stop:
    • Bytes 0-19 = started playback of waveform 1-20
    • Bytes 20-39 = stopped playback of waveform 1-20
  • The AudioPlayer module returns a byte (1) to confirm that it has finished setting events.
• 'T' (ASCII 84): Set trigger mode. 'T' (byte 0) is followed by:
  • Byte 1: The trigger mode index:
    • 0 = Standard mode ('P' command starts playback, 'P' commands received during playback are ignored)
    • 1 = Master mode ('P' command starts playback, 'P' commands received during playback start different waveforms)
    • 2 = Toggle mode ('P' command starts playback, 'P' commands received during playback ends playback)
  • The AudioPlayer module returns a byte (1) to confirm that it has finished setting the trigger mode.
• 'N' (ASCII 78): Return system constants. Nothing follows byte 'N'. The module replies with the following sequence of bytes:
  • liveMode (1 byte); Corresponds to firmware type (0 = AudioPlayer, 1 = AudioPlayerLive)
  • maxWaves (2 bytes; 16-bit int); maximum number of waveforms supported
  • maxEnvelopeSize (2 bytes; 16-bit int); maximum number of samples in AM envelope
  • maxSamplingRate (4 bytes; 32-bit int); maximum sampling rate permitted

Examples

Play sound #4 using an ArCOM serial object in MATLAB:

D = ArCOMObject('COM3', 115200);
D.write(['P' 3], 'uint8'); % Remember that sound position is 0-indexed!
clear D

Trigger sound #4 from the Bpod state machine

LoadSerialMessages('AudioPlayer1', {['P' 3]}); % Set serial message 1

sma = NewStateMachine();

sma = AddState(sma, 'Name', 'PlaySound', ...
    'Timer', 0.1,...
    'StateChangeConditions', {'Tup', 'exit'},...
    'OutputActions', {'AudioPlayer1', 1}); % Sends serial message 1

SendStateMachine(sma);
RawEvents = RunStateMachine;