Telos NX12 - Manual (Page 81)

deTaIled ConfIguraTIon & referenCe | 71
5.11 System Signal Flow and Audio Processing
Send Audio Processing
The Nx12’s send-to-caller audio processing consists of the following functions:
Sample rate conversion
♦
High-pass filter
♦
Frequency shifter
♦
Send AGC/Limiter
♦
Sample Rate Conversion
AES and Livewire sources are sample rate converted to the Nx12’s internal sample rate of 8kHz.
All inputs are re-clocked to the Nx12’s internal clock (derived from the ISDN clock if at least
one ISDN BRI is present).
High-Pass filter
A high pass filter with a 300Hz break frequency improves hybrid performance and enhances
intelligibility by removing unnecessary low-frequencies from the input audio. This function is
always enabled.
Frequency Shifter
A Telos innovation, the frequency shifter (pitch shifter) inserts a small, unnoticeable, shift in
frequency to the send audio to prevent feedback buildup when the system is used with open
speakers.
Send Automatic Gain Control / Limiter
This AGC helps maintain consistent audio levels to the caller. This function is always enabled.
This benefits from a carefully-crafted algorithm utilizing a feed-forward topology with near in-
audible artifacts below the limit threshold. At moderate levels it is ‘AGC-like’ while at high peak
levels it is ‘limiter-like’. In addition to making levels more consistent to callers, this performs the
protection limiting required to meet Telecom regulations.
Receive (Caller) Audio Processing
The Nx12’s receive audio processing consists of the following functions:
High-pass “hum” filter
♦
Duck
Control
X
X Receive
AGC
DDEQ SRC
SRC
Fdbk
Reduce
Send
AGC
A/D
AES
D/A
AES
Adaptive FIR
-
HP
Filter
Input Level
Output Level
ISDN
Telco
Analog
Telco
LW 100BT Analog
Hybrid