# Sound — Functions for audio¶

Note

located in sound.jl

This module contains functions intended to process acoustic samples.

## RIFF/WAVE Functions¶

These functions are used for loading and saving RIFF/WAVE (wav) functions. The API is very similar to the one found in MATLAB.

Here is a quick example that copies an existing file:

julia> require("sound")

julia> using Sound

julia> in_filename = ARGS[1]

julia> y, Fs, nbits, extra = wavread(in_filename)

julia> wavwrite(y, Fs, nbits, strcat("out-", in_filename))


Note

This implementation only supports little endian machines right now.

Reads and returns the samples from a RIFF/WAVE file. The samples are converted to floating point values in the range from -1.0 to 1.0 by default. The io argument accepts either an IO object or a filename (String). The options are passed via an Options object (see the OptionsMod module).

The available options, and the default values, are:

• format (default = double): changes the format of the returned samples. The string double returns double precision floating point values in the range -1.0 to 1.0. The string native returns the values as encoded in the file. The string size returns the number of samples in the file, rather than the actual samples.
• subrange (default = Any): controls which samples are returned. The default, Any returns all of the samples. Passing a number (Real), N, will return the first N samples of each channel. Passing a range (Range1{Real}), R, will return the samples in that range of each channel.

The returned values are:

• y: The acoustic samples; A matrix is returned for files that contain multiple channels.
• Fs: The sampling frequency
• nbits: The number of bits used to encode each sample
• extra: Any additional bytes used to encode the samples (is always None)

The following functions are also defined to make this function compatible with MATLAB:

wavread(filename::String) = wavread(filename, @options)

wavwrite(samples, io[, options])

Writes samples to a RIFF/WAVE file io object. The io argument accepts either an IO object or a filename (String). The function assumes that the sample rate is 8 kHz and uses 16 bits to encode each sample. Both of these values can be changed with the options parameter. Each column of the data represents a different channel. Stereo files should contain two columns. The options are passed via an Options object (see the OptionsMod module).

The available options, and the default values, are:

• sample_rate (default = 8000): sampling frequency
• nbits (default = 16): number of bits used to encode each sample
• compression (default = WAVE_FORMAT_PCM): The desired compression technique; accepted values are: WAVE_FORMAT_PCM, WAVE_FORMAT_IEEE_FLOAT

The type of the input array, samples, also affects the generated file. “Native” WAVE files are written when integers are passed into wavwrite. This means that the literal values are written into the file. The input ranges are as follows for integer samples.

N Bits y Data Type y Data Range Output Format
8 uint8 0 <= y <= 255 uint8
16 int16 –32768 <= y <= +32767 int16
24 int32 –2^23 <= y <= 2^23 – 1 int32

If samples contains floating point values, the input data ranges are the following.

N Bits y Data Type y Data Range Output Format
8 single or double –1.0 <= y < +1.0 uint8
16 single or double –1.0 <= y < +1.0 int16
24 single or double –1.0 <= y < +1.0 int32
32 single or double –1.0 <= y <= +1.0 single

The following functions are also defined to make this function compatible with MATLAB:

wavwrite(y::Array) = wavwrite(y, @options)
wavwrite(y::Array, Fs::Real, filename::String) = wavwrite(y, filename, @options sample_rate=Fs)
wavwrite(y::Array, Fs::Real, N::Real, filename::String) = wavwrite(y, filename, @options sample_rate=Fs nbits=N)