L U C I D SRC9624
Changing Rates In An Ever-changing World
by David Miles Huber

  For those who work largely in the digital domain and routinely handle all types of digital media and formats, the interfacing of the various tools and toys is an increasingly important part of production. Lucid’s SRC9624 can ease the pain of getting digital devices to communicate in a fast-paced studio environment.

The 2-channel SRC9624 is a digital audio sample-rate converter meant for playback, mastering, post-production, broadcast, and any application that demands a broad range of sample-rate, bit-rate, and I/O interface capabilities. The SRC9624 essentially serves as a digital converter/patch bay that can convert any sample rate between 32 and 100 kHz (with either a 16-, 20-, or 24-bit word length) to a wide range of output rates and formats, including a few that you probably never knew existed.

 The Box
SRC9624

SRC9624’s 1U rackspace design (click for larger view).
The SRC9624’s 1U rackspace design sports a brushed-aluminum, sculptured faceplate with a clean, understated layout that lends it an elegance not often encountered in this type of device. Functionally, it has two digital input and output paths (A and B). Each covers the standard digital audio connection types by offering a professional AES port (XLR), a consumer coaxial S/PDIF port, and an optical Toslink S/PDIF port. The unit’s coaxial connectors are of the BNC type (a standard often found on broadcast equipment). Lucid made it easy to connect the unit to consumer digital devices by including BNC-to-RCA adapters.

The front panel provides columns of status LEDs for the unit’s five functional groups: Routing, Input A, Input B, Output Sample Rate, and Output Dither (see Fig. 1). A tiny toggle switch in each section lets you cycle forward or backward through the settings.

Getting There From Here
 The Routing section lets you switch the SRC9624 between four operating modes. In Independent mode, the two digital paths are kept separate; each input is routed to its own output. The Distribution mode routes the input of path A to the output paths of both A and B. The 96 kHz Dual (2>1) mode takes a stereo 96 kHz dual AES signal that has been split between two cables and converts it into any standard format, at any sample rate. And 96 kHz Dual (1>2) takes any standard format, at any rate, and converts it to a stereo 96 kHz dual AES signal.

Many people have never heard of a stereo 96 kHz dual AES signal. Transmitting digital audio over a twisted-pair AES line (usually an XLR mic cable) works just fine for sample rates up to 50 kHz. However, at higher rates, the signal can degrade over longer cable runs. To get around this problem, the AES standard was amended to allow transmission of stereo sample rates above 50 kHz (such as 24/96) over two synchronized AES cables (with one cable carrying the left-channel data and the other carrying the right-channel data).

The front panel’s Input A and Input B sections indicate whether the signal is in a pro (AES) or consumer (S/PDIF) data format and whether it is audio or nonaudio data (for instance, an AC3 surround bitstream). They also let you choose between independent AES, S/PDIF, and optical input connections.

The Output Sample Rate section lets you select from rates of 32, 44.1, 48, 88.2, and 96 kHz. You can also pick any output or pull-down rate between 32 and 100 kHz by synching the rate to an external clock source.

The Output Dither section allows all word lengths to be passed without dither. However, you can dither high-bit-rate input signals down to either 16 or 20 bits using a flat, triangular PDF dither (with no noise shaping) form. This can increase the converted data’s overall dynamic range, albeit with a very low level of dithered noise distributed through audible frequency ranges.

NEXT



 Reprinted with permission from Magazine, December, 2000
© 2000, Intertec Publishing, A Primedia Company All Rights Reserved


[an error occurred while processing this directive]