Auto-Attendant Messages, On-Hold Music and On-Hold Audio for business telephone systems, often called PBX systems, private exchanges or switching systems.
I can provide music, voiceovers and audio in the u-law wav type format often used by these systems. A normal WAV or MP3 file will often not work.
Popular audio format for PBX Systems
- Channels: Mono (1)
- Sample rate: 8000Hz
- Bit depth: 8 bit u-law
- Format: WAV
Sometimes a 16bit mono file at 8Hz can be used
- Channels: Mono (1)
- Sample rate: 8000Hz
- Bit depth: 16 bit
- Format: WAV
Digital Audio Terminology
Bit depth:
The number of ‘bits” of data in each sample
Sample rate:
The number of times the audio is sampled per second
Bit rate:
Bit depth x Sample rate
BPS:
Bits per second
KBPS:
Kilobits per second
- For example CD Audio is 2 channel (stereo) 16 bit at sampling rate of 4 4.1kHz, which equals 1411.2kbps (2 x 16 x 44.1)
- The first example above: mono 8bit 8kHz – gives a bit rate of 64kbps (1 x 8 x 8)
- The second format above: mono 8kHz 16bit – gives a bit rate of 128kbps (1 x16 x 8)
Why is (was) 44.1kHz such a popular sample rate?
This has do with the theorem developed by Nyquist and Shannon in the 1940s, that states that to accurately record a sound digitally, a sample rate of twice its frequency is required. As human hearing at its very best can go up to 20kHz, a sample rate of at least 40kHz is needed and which is covered by the CD sampling rate of 44.1 kHz