10
User's Guide ADI-8 DD © RME
6.3 Input State Display
The input state is displayed by 16 LEDs. Every input has its own SYNC LED. However a miss-
ing or invalid input signal is indicated by slow flashing of the SOURCE LED. As soon as a valid
input signal is present the four SYNC LEDs will react per input. If ADAT or TDIF are chosen as
input source, all four SYNC and Emphasis LEDs show the same information. In DS mode, both
two and two LEDs show the state of the MAIN (1/2) and the AUX (3/4) inputs.
If a valid input signal is applied, SyncCheck is active automatically. When more than one input
signal is present, the input with the lowest number serves as reference. If the AES input is not
chosen as clock source, SyncCheck takes the chosen clock as reference and compares it with
the input clocks. Inputs which are not synchronous will be signalled by quick flashing of the
corresponding SYNC LED.
AES/EBU, SPDIF and TDIF can contain an Emphasis information. Audio signals with Emphasis
have a strong high frequency boost and thus require a high frequency attenuation on playback.
If one of the inputs detects Emphasis, this information is being set at the TDIF output (and be-
ing transmitted correctly to a DTRS machine). Note that the alerting red colour of the Emphasis
LEDs has a reason:
Emphasis is not available within the ADAT standard! This information is thus neither passed
on to the ADAT output, nor taken into account later on for acoustic transmission!
Each channel's audio level is shown by a LEVEL LED. The green LED becomes active from -
90 dBFS and above, a higher level yields brighter light. Thus only one LED is necessary to see
if there is an audio signal or digital zero, only noise floor or a meaningful signal.
6.4 Sample Rate Conversion
Each AES/EBU input has its own sample rate converter (SRC). An SRC allows for a conversion
of the sampling rate in real-time. The 24 bit SRCs used in the ADI-8 DD work virtually without
loss, i. e. there are no audible artefacts or noise signals. The SRC works so well that we could
recommend to leave it switched on all the time, and thus eliminate any clock problem in the
first place.
The ADI-8 DD's SRC yields a maximum conversion ratio of 3:1 or 1:3. 96 kHz can be con-
verted to any sample rate down to 32 kHz, 32 kHz to any rate up to 96 kHz.
If the internal clock is being used, the SRC works as a perfect jitter killer. But the ADI-8 DD
allows for any source as clock reference (except AES/EBU). With other settings than INT, the
device is slave as usual, and the jitter of the output signal thus is depending on the jitter of the
clock source.
An SRC is not only being used for conversion of sample rates and jitter suppression, it is espe-
cially useful for the so-called clock decoupling. By means of an SRC, any device which can't be
synchronized (CD-Player, consumer DAT etc.) can be used within a digital audio network as if it
was synchronizable. The SRC decouples any input clocks and sets the output clock to the
common reference (no matter which one), thus allows for bringing together various clock
sources without any clicks or drop-outs.
Further information on sample rate conversion can be found in chapter 11, Technical Back-
ground.
