Dolby Laboratories Lake LP4D12, Руководство пользователя

Страница: 59 / 68

Dolby
®
Lake
®
Processor System Manual
47
Chapter 7
Connecting Digital Audio Devices
Connecting multiple digital audio devices has always been a complex subject. With
the variety of sample rates commonly utilized for various transport protocols and
storage media, the practitioner must juggle multiple differing requirements.
Additionally, the demands of live sound and multimedia studio production may
require mix stems at multiple sample rates for multiple destinations.
All of these connection issues are typically addressed through the use of a sample-rate
converter on both digital input and digital output channels. Sample-rate converters
allow an incoming or outgoing signal to run at a sample rate that is independent of the
signal processing in an audio device.
A high-quality sample-rate converter introduces significant latency. This latency is
the result of collecting a relatively large number of samples in order to derive a new
set of samples at the desired sample rate. Latencies on the order of 5 to 10
milliseconds per conversion stage are common, resulting in an overall latency through
a sample-rate conversion system of up to 20 milliseconds.
The additional latency incurred by sample-rate converters is unacceptable in many
live sound applications. One millisecond is approximately equivalent to a sound
propagation distance of one foot, so a five-millisecond latency translates into five
feet. An additional latency of five milliseconds is unacceptable in live sound monitor
applications, as the delay affects the artist’s subjective perception. If two sample-rate
conversions are required, resulting in a latency exceeding ten milliseconds, the delay
incurred will begin to sound like an echo to the performer (quite a bad thing for
artists, especially percussionists).
The Dolby
®
Lake
®
Processor introduces a new patent-pending technique that reduces
the required latency significantly, regardless of sample rate. In addition to low latency
conversion, the Processor prioritizes and synchronizes incoming and outgoing signals
at different sample rates on each pair of digital inputs and outputs.
This chapter describes how to connect the Processor to other digital audio devices.
7.1 Internal and External Clocks
The Dolby Lake Processor provides two fully independent clock systems in order to
provide a very flexible and robust audio processing system. The Primary Clock
Source and Sample Rate Converter Clock Source work together to provide a digital
audio system capable of receiving and transmitting 44.1, 48, 88.2, 96, 176.4, and