Huron & SNAP Documentation

HURON TECHNICAL REFERENCE
• Always use the pre-amplifier in preference to the volume
control to boost lower level analogue inputs. It is always
preferable to increase the analogue signal level as much as
possible at the pre-amplifier to avoid an unnecessary noise
contribution at the input to the volume control.
• Always aim to provide a near full scale input signal to the
A/D converter, by using the appropriate gain settings in the
pre-amplifier and the volume control.
• The volume control should not generally be used to attenuate
the analogue input signal. Any reduction in the signal level
through the volume control may mean that clipping at the
pre-amplifier output, due to excessive input signal level, will
go undetected at the A/D input.
The following analogue input control settings are
recommended:
Input signal type Typical signal Pre-amplifier Volume
level
setting
Control setting
Professional Line Level +20dBm 0dB 0dB
Professional Line Level +14dBm 0dB 6dB
Consumer Line Level +0dBm 20dB 0dB
Dynamic Microphone -20dBm 40dB 0dB
Audio Output Levels
The digital output module in the system contains an 18-bit D/A
converter and a volume control to provide the capability for
driving analogue output levels less than the maximum 20dBm.
The analogue outputs are electronically balanced. A schematic
of the audio output circuit (on the D/A module) is shown below:
Figure 107 — D/A output schematic
The volume control settings on the D/A modules are
manipulated by the upper row of sliders in the I/O Manager
Tool.
The following recommendations apply to the use of the D/A
output module:
• Always aim to supply a digital signal to the D/A converter
that is close to full scale signal levels. If the digital output
signal is scaled down significantly below full scale, it will
lead to a reduction in the signal-to-noise performance of the
D/A converter.
HURON TECHNICAL MANUAL PAGE 302