spandsp: MFC/R2 tone receiver

spandsp 0.0.6

MFC/R2 tone receiver

# What does it do?

The MFC/R2 tone receiver module provides for the detection of the repertoire of 15 dual tones needs for the digital MFC/R2 signalling protocol. It is compliant with ITU-T Q.441D.

# How does it work?

Basic MFC/R2 tone detection specs:

- Receiver response range: -5dBm to -35dBm
- Difference in level for a pair of frequencies
  - Adjacent tones: <5dB
  - Non-adjacent tones: <7dB
- Receiver not to detect a signal of 2 frequencies of level -5dB and duration <7ms.
- Receiver not to recognise a signal of 2 frequencies having a difference in level >=20dB.
- Max received signal frequency error: +-10Hz
- The sum of the operate and release times of a 2 frequency signal not to exceed 80ms (there are no individual specs for the operate and release times).
- Receiver not to release for signal interruptions <=7ms.
- System malfunction due to signal interruptions >7ms (typically 20ms) is prevented by further logic elements.