ART Pro Audio DIO - A/D Converter - Manual (Page 5)

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SAMPLE RATE LED INDICATORS
The Sample Rate LED Indicators show the current sample rate that the
DI/O’s A/D and D/A are operating at. When set to one of the internally
generated sample rates (44.1, 48, 88.2, or 96kHz), the DI/O provides
the Master clock source from its internal crystal clock.
When set to the External Sync position, the DI/O will use the S/PDIF In
jack as the source of its Master clock. It will synchronize to, and track,
sample rates from 22kHz to 100kHz. The green (Ext.) LED indicator
will light solid as long as the source has valid audio sync. It will flash if
the data on the S/PDIF input jack does not contain valid audio data.
When this occurs the D/A will mute its audio outputs to prevent
unwanted noise. The A/D will still digitize audio and track the external
Master clock.
SIGNAL LEVEL LED INDICATORS
The three Signal Level LED Indicators are designed to help set levels
before the A/D, to maximize your dynamic range.
The green (-20dB) LED comes on when the signal at the A/D is 20dB
below full-scale digital clipping on signal peaks. It just starts to come on
when the average signal is around 30dB below clipping. You should
increase your input signal level, or the DI/O’s Input Gain until this light
is on solid whenever there is signal for best performance.
The red (0dB) LED comes on when the signal at the A/D is 3dB away
from full-scale clipping. With most audio material, you would increase
the input signal or Input Gain until this light just starts to come on
during signal peaks.
The yellow (Warm) LED comes on whenever the tube is adding
warmth or character to the signal. This is a function of both the input
signal level and the Tube Warmth control.