WAV
Waveform Audio File Format is an audio format with a .wav file extension, used by all of Valve's engines. It is required for lipsynced dialogue and looped sounds without a custom audio backend.
GoldSrc supports uncompressed 8-bit or 16-bit PCM, although lip-synched audio must be 8-bit. It supports sample rates of 11025 Hz or 22050 Hz; other sample rates can sometimes be used, but they will be resampled to 22050 Hz before playback, without any interpolation.
Source supports uncompressed 8-bit and 16-bit PCM, as well as compressed 4-bit Microsoft ADPCM (not IMA). It supports sample rates at 11025 Hz, 22050 Hz, and 44100 Hz; files at other sample rates, such as 32000 Hz and 48000 Hz, will not play.
Note:Custom audio backends, such as MetaAudio or FMOD can extend the range of supported sample rates and bit depths.
Confirm:What about 
Source 2? It definitely supports 16-bit 44.1 KHz WAVs (mono and stereo), but does it support the other formats that and support?It supposedly supports arbitrary sample rates for MP3s; is this the case for WAVs as well?
Bug:Files using the extended Broadcast Wave Format (BWF) have weird behavior in Source, and should be converted to regular WAV using FFmpeg or Audacity before use in-game. Some audio editors export as BWF automatically, such as Pro Tools and Logic Pro, and do not provide an option to export a standard WAV. [todo tested in?]
Warning:Although the WAV format specifications permit up to 32 channels in a single file, and supports surround sound, does not support WAV files with more than 2 channels!Bit rates
WAV files have a consistent bitrate depending upon their sample rate, bit depth, and channel count. The following tables indicate what bitrates files will be at supported sample rates.
Tip:Bitrate = Sample Rate * Bit Depth * Channel CountMono sounds (1 channel)
| Sample Rate | 16-bit PCM | 8-bit PCM | 4-bit ADPCM | Quality |
|---|---|---|---|---|
| 11025 Hz | 176.4 kbps | 88.2 kbps | 44.1 kbps | AM radio; used by most  sound effects
|
| 22050 Hz | 352.8 kbps | 176.4 kbps | 88.2 kbps | Max sample rate of sound effects
|
| 44100 Hz | 705.6 kbps | 352.8 kbps | 176.4 kbps | CD quality |
Stereo sounds (2 channels) (not in )
| Sample Rate | 16-bit PCM | 8-bit PCM | 4-bit ADPCM | Quality |
|---|---|---|---|---|
| 11025 Hz | 352.8 kbps | 176.4 kbps | 88.2 kbps | AM radio |
| 22050 Hz | 705.6 kbps | 352.8 kbps | 176.4 kbps | |
| 44100 Hz | 1411.2 kbps | 705.6 kbps | 352.8 kbps | CD quality |
Some games (particularly third-party ones) may support additional sample rates and bit depths, but the above sample rates are supported by all Source games.
Tip:(only in ) If lower file sizes are desired, MP3 files can also be used in some situations; see Compression (Source 1)#Audio Compression for comparisons.