scipy.io.wavfile.read

scipy.io.wavfile.read(filename, mmap=False)

Open a WAV file.

Return the sample rate (in samples/sec) and data from an LPCM WAV file.

Parameters

filenamestring or open file handle

Input WAV file.

mmapbool, optional

Whether to read data as memory-mapped (default: False). Not compatible with some bit depths; see Notes. Only to be used on real files.

New in version 0.12.0.

Returns

rateint

Sample rate of WAV file.

datanumpy array

Data read from WAV file. Data-type is determined from the file; see Notes. Data is 1-D for 1-channel WAV, or 2-D of shape (Nsamples, Nchannels) otherwise. If a file-like input without a C-like file descriptor (e.g., io.BytesIO) is passed, this will not be writeable.

Notes

Common data types: [1]

WAV format	Min	Max	NumPy dtype
32-bit floating-point	-1.0	+1.0	float32
32-bit integer PCM	-2147483648	+2147483647	int32
24-bit integer PCM	-2147483648	+2147483392	int32
16-bit integer PCM	-32768	+32767	int16
8-bit integer PCM	0	255	uint8

WAV files can specify arbitrary bit depth, and this function supports reading any integer PCM depth from 1 to 64 bits. Data is returned in the smallest compatible numpy int type, in left-justified format. 8-bit and lower is unsigned, while 9-bit and higher is signed.

For example, 24-bit data will be stored as int32, with the MSB of the 24-bit data stored at the MSB of the int32, and typically the least significant byte is 0x00. (However, if a file actually contains data past its specified bit depth, those bits will be read and output, too. [2])

This bit justification and sign matches WAV’s native internal format, which allows memory mapping of WAV files that use 1, 2, 4, or 8 bytes per sample (so 24-bit files cannot be memory-mapped, but 32-bit can).

IEEE float PCM in 32- or 64-bit format is supported, with or without mmap. Values exceeding [-1, +1] are not clipped.

Non-linear PCM (mu-law, A-law) is not supported.

References

1

IBM Corporation and Microsoft Corporation, “Multimedia Programming Interface and Data Specifications 1.0”, section “Data Format of the Samples”, August 1991 http://www.tactilemedia.com/info/MCI_Control_Info.html

2

Adobe Systems Incorporated, “Adobe Audition 3 User Guide”, section “Audio file formats: 24-bit Packed Int (type 1, 20-bit)”, 2007

Examples

>>> from os.path import dirname, join as pjoin
>>> from scipy.io import wavfile
>>> import scipy.io

Get the filename for an example .wav file from the tests/data directory.

>>> data_dir = pjoin(dirname(scipy.io.__file__), 'tests', 'data')
>>> wav_fname = pjoin(data_dir, 'test-44100Hz-2ch-32bit-float-be.wav')

Load the .wav file contents.

>>> samplerate, data = wavfile.read(wav_fname)
>>> print(f"number of channels = {data.shape[1]}")
number of channels = 2
>>> length = data.shape[0] / samplerate
>>> print(f"length = {length}s")
length = 0.01s

Plot the waveform.

>>> import matplotlib.pyplot as plt
>>> import numpy as np
>>> time = np.linspace(0., length, data.shape[0])
>>> plt.plot(time, data[:, 0], label="Left channel")
>>> plt.plot(time, data[:, 1], label="Right channel")
>>> plt.legend()
>>> plt.xlabel("Time [s]")
>>> plt.ylabel("Amplitude")
>>> plt.show()