Audio Waveform File Formats
- Microsoft .WAV File Format
- .au File Format
- Hypersignal Waveform File Format
- Speech Codec Wav Files ◳
Microsoft Waveform File Format
The "standard" Microsoft .WAV file format, unless modified by user defined extension, is exclusively a time domain format. This includes .WAV files typically used with WinXP and other versions of Window and popular off-the shelf multimedia products. The standard format contains a simple 44-byte header, which allocates no values for frequency domain information, wavelet domain information, or other math/DSP analysis purposes. Although the .WAV format is theoretically a subset of the general Microsoft RIFF format, and can thus be extended to contain user-defined header and data sections, experience shows that many off-the-shelf software packages fail to safely ignore non-standard sections, and may crash or process incorrect data.One significant advantage of the .WAV format is inclusion of the "Format/Compression" header attribute, which provides support for a range of PCM and compressed data types, ranging from 16-bit linear to voice codec such as G.729, ADPCM, iLBC, and others.
Below is a quick reference for the standard .WAV file format. See the Microsoft Windows Multimedia Programmer's Reference, chapter 8, for detailed information on the .WAV format.
Table 1, Microsoft WAVE File Format Quick Reference
|
Name |
Word Offset 1 |
Size / Type |
|
SHORT HEADER |
||
|
'RIFF' section tag 2 |
0 |
4 bytes |
|
Length of RIFF section |
2 |
doubleword |
|
'WAVE' Format Identifier |
4 |
4 bytes |
|
'fmt ' section tag |
6 |
4 bytes |
|
Length of fmt section |
8 |
doubleword |
| Format/Compression | 10 (See table below for details) | word |
|
Number of Channels |
11 |
integer |
|
Sampling Frequency (in Hz) Average Bytes Per Second 3 Block Alignment 4 |
12 14 16 |
doubleword doubleword integer |
|
Precision (Number of bits per sample, typically 8 or 16) |
17 |
word |
'data' section tag Length of data section (NB) Start of Waveform Data |
18 20 22 |
4 bytes doubleword NB/2 words |
_______________________________________________________________________________________________ Total 44 bytes |
||
Notes
1 Unless otherwise mentioned, words are 16-bit unsigned integers ranging in value from 0..65535, integers are 16-bit values ranging from -32768..32767, doublewords are 32-bit unsigned integers ranging in value from 0..4294967295, singles are IEEE format 32-bit floating-point values, and doubles are IEEE format 64-bit floating-point values.
2 Header elements enclosed in single-quote marks indicate actual, exact text in the .WAV header.
3Avg bytes per sec is typically determined by the formula:
Avgbps = Number of channels * Sampling Frequency * (Precision >> 3)
4 Block Alignment is typically given by the formula:
blkalign = Number of channels * (Precision >> 3)
Wav Header Limitations
There are several limitations to the de facto standard 44-byte header .WAV format found in use with many multimedia programs. One of the most noticeable is the lack of maximum amplitude value, which causes .WAV files to be displayed and processed in Hypersignal and other signal analysis software as if they always contained full-scale values. Another is lack of frequency or wavelet domain information. These are limitations when working with Hypersignal or DirectCore® software. When using these software packages, it is recommended to convert .WAV files into Hypersignal .TIM format one of the following ways:
1. Use the Wav2Tim conversion function in Hypersignal Macro.
2. Use File Acquisition function in Hypersignal.
3. Use the .WAV file as direct input into Hypersignal or DirectCore function, by specifying the .WAV extension explicitly in an input waveform filename field.
Table 2, WAVE File Header Format/Compression Codes
Code |
Format/Compression Type |
0x0000 |
unknown |
0x0001 |
Linear PCM/uncompressed |
0x0002 |
Microsoftt ADPCM |
0x0003 |
IEEE floating-point |
0x0005 |
IBM CVSD |
0x0006 |
Microsoft ALAW (8-bit ITU-T G.711BA ALAW) |
0x0007 |
Microsoft M-LAW (8-bit ITU-T G.711 M-LAW |
0x0011 |
Intel IMA/DVI ADPCM |
0x0016 |
ITU G.723 ADPCM |
0x0017 |
Dialogic OKI ADPCM |
0x0030 |
Dolby AAC |
0x0031 |
Microsoft GSM 6.10 |
0x0036 |
Rockwell ADPCM |
0x0040 |
ITU G.721 ADPCM |
0x0042 |
Microsoft MSG723 |
0x0045 |
ITU-T G.726 |
0x0064 |
APICOM G.726 ADPCM |
0x00101 |
IBM M-LAW |
0x00102 |
IBM A-LAW |
0x00103 |
IBM ADPCM |