General |
The main body of AES3 specifies signal transmission via a single shielded twisted wire pair. Annex D, however, discusses the carriage of AES3 signals on structured wiring, e.g., the "category 5" cables associated with computer network installations, a topic that receives extended treatment in AES47, which specifies the method of carrying multiple channels of audio in linear PCM or AES3 format across an asynchronous transfer mode (ATM) network. Elaborations on audio signal transfer are the topics of AES10-2003, AES Recommended Practice for Digital Audio Engineering 8221; Serial Multichannel Audio Digital Interface (MADI) (Revision of AES10-1991), and AES50-2005: AES standard for digital audio engineering 8221; High-resolution multi-channel audio interconnection.
Certain sampling frequencies are recommended by the AES in AES5, pp. 5-6:
- The recommended sampling frequency for digital audio encoding shall be 48 kHz ± 10 parts per million. This frequency is compatible with television and motion picture systems, and it permits the encoding of audio programs with full 20-kHz bandwidth. It is recommended for all applications of program origination, processing, and interchange. To maintain synchronization whenever digital audio using the standard 48-kHz sampling frequency is utilized in conjunction with television or motion pictures, the average number of samples per frame shall be [as follows: nominal frame rate of 24, then 2,000 samples per frame; 25 frames, then 1,920 samples; 30 frames, 1,600 samples; and 30/1,001 frames, 8008/5 samples].
- For an application directly related to certain consumer products, a sampling frequency of 44,1 kHz may be used. This application may include the interchange of program material prepared specifically for such products.
- For broadcast and transmission-related applications with restricted channel capacity and where a nominal audio bandwidth of 15 kHz is considered adequate, a sampling frequency of 32 kHz may be used, in accordance with ITU-T Recommendation J.53.
- For applications with an audio bandwidth greater than 20 kHz or in order to permit the use of a wider transition region in the anti-alias filtering a rate of 96 kHz ± 10 parts per million may be used.
- Techniques have come into common use since the above frequencies were defined which use very high sampling frequencies, typically more than 100 times higher than 48 kHz. Where such sampling frequencies appear at an interface, only multiples representing some factor of two of the sampling frequencies identified in AES5 should be used.
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