Survey of Sound class 9
esse quam videri
Sampling theory
Quantization Error
- Difference between the actual analog value and the quantized digital value due to rounding (or truncating)
aka signal to error ratio
Aliasing
- Error due to under sampling
Nyquist Sampling Rate = 2 * highest frequency
- http://en.wikipedia.org/wiki/Nyquist_rate
- http://www.dsptutor.freeuk.com/aliasing/AD102.html
- http://en.wikipedia.org/wiki/Wagon-wheel_effect
- http://en.wikipedia.org/wiki/Nyquist_frequency
Jitter
- Time synchronization error
Bit Depth
over 24 bit used mainly for internal processing and really high end audio equipment 24 bit Professional recording and internal processing 16 bit CD quality audio (not so good for processing) 8 bit Smaller size used for consumer voice stuff and multimedia
Sampling Rates
Some Common Sampling Rates
| Sampling Rate | Use |
|---|---|
| 2,822,400 Hz | SACD |
| 192kHz | Professional recording |
| 96kHz | Professional recording Modern Sound Cards HDDVD BlueRay SACD etc |
| 48 kHz | Professional recording (commonly used for TV/film) |
| 44.1 kHz | CD quality Audio |
| 32 kHz | miniDV digital video camcorder, DAT (LP mode) |
| 22 kHz | lower-quality PCM and MPEG audio |
| 11 kHz | Multimedia/ Games |
| 8 kHz | telephone, adequate for human speech |
http://en.wikipedia.org/wiki/Sampling_rate
File Size per Sampling rate and Bit Depth
| Sample Rate | Bit Width | File Size per minute |
| 96 kHz | 24-bit Stereo | 33.0 MB |
| 44.1 kHz | 16-bit Stereo | 10.5 MB |
| 44.1 kHz | 16-bit Mono | 5.3 MB |
| 44.1 kHz | 8-bit Stereo | 5.3 MB |
| 44.1 kHz | 8-bit Mono | 2.6 MB |
| 22 kHz | 16-bit Stereo | 5.3 MB |
| 22 kHz | 16-bit Mono | 2.6 MB |
| 22 kHz | 8-bit Stereo | 2.6 MB |
| 22 kHz | 8-bit Mono | 1.3 MB |
| 11 kHz | 16-bit Stereo | 2.6 MB |
| 11 kHz | 16-bit Mono | 1.3 MB |
| 11 kHz | 8-bit Stereo | 1.3 MB |
| 11 kHz | 8-bit Mono | 660 KB |
Note : Dropping the Sampling Rate or Bit Depth by half leads to half the file size
Audio File formats
| name | ext. | info |
|---|---|---|
| aiff | .aif | audio interchange file format (mac native) supports markers and regions |
| sd2 | .sd2 | sound designer 2 (digidesign native) supports markers and regions |
| wave | .wav | wave file (Microsoft) many different formats most support markerz and regions |
| au-law | .au or .aul | au-law file (unix native) supports compression |
| RAM | .ram or .ra | Real audio File supports compression and streaming |
| Mpeg3 | .mp3 | Mpeg layer 3 supports variable compression and streaming (AMP) |
| AAC | .aac | Mpeg2 Advanced Audio Coding AC-3 standard NEW not supported yet http://www.execpc.com/%7Ereal/aac/index.html |
| MIDI | .mid | not and audio format |
| Modular (MOD) | .mod | kinda an audio format (used mainly for games) |
| ASF wmv | .asf .wmv | windows Media and Advanced Streaming Format Microsoft supports variable compression streaming video encryption |
CD Formats
- RedBook Audio standard CD audio format
- CDROM-XA (eXtended Archetecture) audio and data
