FX609, FX619 and FX629 FAQ
Q. 609 - How do you perform clock recovery when transmitting audio data on an RF channel using the FX6x9 CODECS?
A. The FX609/619/629 Codecs use Delta Modulation where the encoded data contains information on the signal amplitude only. The sampling frequency must be equal during both encoding and decoding to preserve the time information of the signal.
On most carriers (RF, Fibre optic, Co-axial wire) it is not practical to send a synchronising clock on a separate link and a method of embedding this is required. CML produce a number of Data Pumps which use synchronous bearer channels where clock recovery is performed at the decoder. These Data Pumps require a preamble to synchronise the receiver's clock with the transmitter's clock. Use can be made of the idle pattern (101010 . . .) on the FX6n9 Codecs to provide this preamble.