User`s manual

ADX-32A / ADX-64A-PRO

5.3. Latency

Latency has – in contrast to traditional analog systems - always been a topic in digital audio

technology. High latency can lead to unwanted effects, such as phasing, hall, echo etc. and can

seriously affect audio performance. One design goal of the ADAT Multicore Extender was to

build a system offering one of the lowest latency values on the market. By design, other digital

snake solutions (e.g. Ethernet based systems) have a relatively high propagation delay, because

audio data has to be sampled, buffered, converted, transmitted, buffered and then finally

converted back to the original format. In contrast, ADAT Multicore Extender uses only minimal

buffering with no data conversion at all, achieving an excellent overall latency of less then 1µs.

5.4. Jitter

In any digital audio transmission, the clock signal picks up a certain amount of jitter (clock phase

noise). One must differentiate between two kinds of jitter (actually, two effects the jitter has on

an audio signal), as described below:

On one hand, there's the so called “sampling jitter”, occurring only at the point of digital-to-

analog conversion or vice versa. Sampling jitter can cause distortion or noise since the time-

domain information of a signal is altered. Today, DACs and ADCs make use of various advanced

re-clocking technologies in order to attenuate the jitter. Well designed equipment is no more

sensitive to sampling jitter regarding audio quality.

On the other hand, when jitter occurs on an interface used for the transmission of the data (e.g.

when used with an ADAT interface), it's called “interface jitter”. This kind is much less critical

since it only has an audible effect if its value is so large that it prevents the proper detection of

bits within the data stream (for AES/EBU, the specification allows a jitter value of ±20ns, which

is about 25% of a bit time). In a properly designed system, such high values should never occur.

To cope with jitter, other systems use often special re-clocking circuitry (Phase Locked Loop,

“PLL”). A PLL has good jitter attenuation characteristics, but must be specially adapted to the

used data format and sample rate in order to achieve optimal results. ADAT Multicore Extender

uses another approach: Instead of transmitting a signal with a relatively large gain of jitter and

then attenuating it with a PLL, it makes use of the most advanced transceiver technology

available, which has a very good out-of-the box jitter performance. The overall jitter of an ADAT

signal transmitted over 330ft (100m) Cat5 cable is only 4ns (typ.) which ensures correct bit

detection with an appropriate safety margin. This approach provides some advantages:

 Very low latency since no buffering is required

 Optimal transmission of arbitrary signals, independently of the encoding or speed

(e.g. ADAT, S/PDIF, AES/EBU, AC-3)