wave_file_format.rar_wav_wave_文件格式

audio interchange file format

wave file format

wave file format is a file format for storing digital audio (waveform) data. it supports a variety of bit resolutions, sample rates, and

channels of audio. this format is very popular upon ibm pc (clone) platforms, and is widely used in professional programs that process

digital audio waveforms. it takes into account some pecularities of the intel cpu such as little endian byte order.

this format uses microsoft's version of the electronic arts interchange file format method for storing data in "chunks".

data types

a c-like language will be used to describe the data structures in the file. a few extra data types that are not part of standard c, but which

will be used in this document, are:

constants

decimal values are referred to as a string of digits, for example 123, 0, 100 are all decimal numbers. hexadecimal values are preceded by

a 0x - e.g., 0x0a, 0x1, 0x64.

data organization

all data is stored in 8-bit bytes, arranged in intel 80x86 (ie, little endian) format. the bytes of multiple-byte values are stored with the

low-order (ie, least significant) bytes first. data bits are as follows (ie, shown with bit numbers on top):

7 6 5 4 3 2 1 0

+-----------------------+

char: | lsb msb |

+-----------------------+

+-----------------------+-----------------------+-----------------------

+-----------------------+

long: | lsb byte 0 | byte 1 | byte 2 |

byte 3 msb |

+-----------------------+-----------------------+-----------------------

+-----------------------+

file structure

a wave file is a collection of a number of different types of chunks. there is a required

which contains important

audio interchange file format

there are

some inflexibly written programs expect the format chunk as the first chunk (after the riff header) although they shouldn't

because the specification doesn't require this.

here is a graphical overview of an example, minimal wave file. it consists of a single wave containing the 2 required chunks, a format

and a data chunk.

__________________________

| riff wave chunk |

| groupid = 'riff' |

| | sound data chunk | |

| | ckid = 'data' | |

| |__________________| |

|__________________________|

a bastardized standard

the wave format is sort of a bastardized standard that was concocted by too many "cooks" who didn't properly coordinate the addition of

"ingredients" to the "soup". unlike with the aiff standard which was mostly designed by a small, coordinated group, the wave format has

had all manner of much-too-independent, uncoordinated aberrations inflicted upon it. the net result is that there are far too many chunks

that may be found in a wave file -- many of them duplicating the same information found in other chunks (but in an unnecessarily

different way) simply because there have been too many programmers who took too many liberties with unilaterally adding their own

i've attempted to document only those aspects that you're very likely to encounter in a wave file. i suggest that you concentrate upon

these and refuse to support the work of programmers who feel the need to deviate from a standard with inconsistent, proprietary, self-

serving, unnecessary extensions. please do your part to rein in half-ass programming.

sample points and sample frames

a large part of interpreting wave files revolves around the two concepts of sample points and sample frames.

a sample point is a value representing a sample of a sound at a given moment in time. for waveforms with greater than 8-bit resolution,

each sample point is stored as a linear, 2's-complement value which may be from 9 to 32 bits wide (as determined by the

wbitspersample field in the format chunk, assuming pcm format -- an uncompressed format). for example, each sample point of a 16-bit

waveform would be a 16-bit word (ie, two 8-bit bytes) where 32767 (0x7fff) is the highest value and -32768 (0x8000) is the lowest

value. for 8-bit (or less) waveforms, each sample point is a linear, unsigned byte where 255 is the highest value and 0 is the lowest

audio interchange file format

from 1 to 8 bits wide, a sample point should be stored in a wave as an 8-bit byte (ie, unsigned char). if your adc produces a sample point

from 9 to 16 bits wide, a sample point should be stored in a wave as a 16-bit word (ie, signed short). if your adc produces a sample point

from 17 to 24 bits wide, a sample point should be stored in a wave as three bytes. if your adc produces a sample point from 25 to 32 bits

wide, a sample point should be stored in a wave as a 32-bit doubleword (ie, signed long). etc.

furthermore, the data bits should be left-justified, with any remaining (ie, pad) bits zeroed. for example, consider the case of a 12-bit

sample point. it has 12 bits, so the sample point must be saved as a 16-bit word. those 12 bits should be left-justified so that they become

bits 4 to 15 inclusive, and bits 0 to 3 should be set to zero. shown below is how a 12-bit sample point with a value of binary

101000010111 is formatted left-justified as a 16-bit word.

___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___

| | | | | | | | | | | | | | | | |

but note that, because the wave format uses intel

___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___

| | | | | | | | | | | | | | | | | |

| 0 1 1 1 0 0 0 0 | | 1 0 1 0 0 0 0 1 |

|___|___|___|___|___|___|___|___| |___|___|___|___|___|___|___|___|

<-------------> <-------------> <----------------------------->

bits 0 to 3 4 pad bits bits 4 to 11

for multichannel sounds (for example, a stereo waveform), single sample points from each channel are interleaved. for example, assume

the sample points that are meant to be "played" (ie, sent to a dac) simultaneously are collectively called a sample frame. in the example

of our stereo waveform, every two sample points makes up another sample frame. this is illustrated below for that stereo example.

sample sample sample

frame 0 frame 1 frame n

_____ _____ _____ _____ _____ _____

| ch1 | ch2 | ch1 | ch2 | . . . | ch1 | ch2 |

|_____|_____|_____|_____| |_____|_____|

_____

| | = one sample point

|_____|

audio interchange file format

audio interchange file format