Vocality V100 Technical Manual page 73

C H A P T E R 3 C O N F I G U R I N G V 1 0 0
MODE
The card may be connected to Analogue or Digital signals and indeed may convert one format to the other
from end to end as configured by the "Mode" parameter. In analog mode, signals up to 0.775vrms may
be connected to the inputs. Output levels are adjusted in the factory to reproduce this from a reference
input. In Digital mode, stereo AES/EBU format data packets are transferred on the LEFT IN/OUT
connectors.
CLOCK REFERENCES
Internally, the sample clock rate is fixed at 48KHz, which may be phase-locked to either the GRXCLK or
the GTXCLK reference busses as selected by the "Sample Clock Ref" field (The encoder and decoder
sample rates are the same since they use the same Real-Time Audio (RTA) interface internally and they
must be the locked at both ends of the V100 link). The sample clock rate is automatically up- or down-
converted to achieve better sound quality at lower bit rates using Sample Rate Converters, to provide 2:1,
3:1, 4:1 or 6:1 up- and down-sampling for compatibility with 48KHz, 32KHz, 24KHz, 16KHz or 8KHz
sample rates in external equipment. They also produce the intrinsic rate of 16KHz used by G.722 and
8KHz used by G.711. In Digital mode, the sample clock is extracted from the incoming AES/EBU data
stream by the encoder and may be used to drive the GRXCLK or GTXCLK bus for onward-linking as
defined by the "AES Clock Ref" field. The decoder at the remote end then restores the AES/EBU clock with
the decoded data. Finally in G.711/G.722 modes the number of samples in each frame may be adjusted
according to the "Frame Length (samples)" field.
CODER TYPE
The "Coder Type" field selects the overall Encoding and Decoding standard. It is possible to set a different
type in each direction, or to disable one direction completely. The "Coder Bit Rate" may be set according
to type. G.711 and G.722 always run at 64Kbps and MPEG allows a wide range from 8Kbps to 448Kbps,
which may be set according to the available bandwidth. An MPEG decoder will automatically follow the
encoder bit rate.
CODER BIT RATE
The "Coder Mode" field is dependent upon the Encoder type. A G.711 encoder may operate in A-Law or u-
Law, always at 64Kbps. A G.722 encoder may only operate in Mode 1 (64K). The available MPEG
encoders vary according to bit rate, Type and Layer. MPEG-1 permits sample rates of 48KHz, 44.1KHz
and 32KHz with selectable encoded rates between 32Kbps and 448Kbps. MPEG-2 achieves similar quality
at half the sample rates, i.e. 24KHZ, 22.05KHz and 16KHz, with encoded data rates of between 8Kbps
and 256Kbps. Layer I of the standard supports the standard MPEG encoding characteristics, while Layer II
uses additional techniques such as psycho-acoustic modelling to reduce the encoded bit rate. The choice is
left to the user.
V100 Versatile Multiplexer Technical Manual Version 2.2
Page 73 of 231