Grass Valley NV8900 Series v.1.3 - Manual (Page 23)

15
NV8900
User’s Guide
Obtaining Software and Documentation
This document is available through the Miranda web site.
Maintenance
The NV8900 requires no maintenance.
Channel Numbering
The MADI interfaces support 64 audio channels, 0–63. The MADI channels are paired on the AES
inputs or outputs.
Use the following formula to calculate a port number, given a MADI channel number:
p = m / 2 + 1 0 ≤ m ≤ 63.
Use the following formulas to calculate a MADI channel pair, given a port number:
m
1
= p × 2 – 2 1 ≤ p ≤ 32.
m
2
= p × 2 – 1
Audio Rates
According to the MADI specification, MADI receivers and drivers operate at 125 MHz which
supports 100M bits per second under 4B5B encoding. The receivers expect and the drivers
produce 64 audio channels at exactly 48
kHz. The 64 channels consume 98,304,000 bps with a
1.7% margin for sync symbols and padding.
At least one sync symbol must accompany every MADI frame. The minimal number of sync
symbols is 48,000 per second. At 10 bits per symbol, that is 480,000 bits out of 2,120,000 spare
bits.
The AES10-2003 specification’s tolerance on the transmission rate is 100 ppm (10
–4
). Thus the
rate must be 125 MHz ± 12,500 kHz.
 Our MADI interfaces send and receive AES at 48.0 kHz exactly. The data rate is, of course,
affected by the actual transmission rate. The effect on a 48 kHz data rate is a variance of ±
4.8 Hz.