Serially transmitted digital data are received in a predetermined format
such as an SPDIF format. In the format, identification data are incorporated in
the serial data in predetermined cycles. Generation of a train of bit-extracting
pulses having a predetermined pulse generation pattern is triggered by detection
of a pulse edge of the received serial data. By counting the bit-extracting pulses,
bit location information is generated which identifies each bit location in the
received serial data. Each identification data is detected from among the received
digital data and the number of detections of the identification data within a predetermined
time period is calculated, so as to identify a transmission rate of the digital
data on the basis of the number of detections.
