Changing rates in an ever-changing world.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 BOXThe 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. A tiny toggle switch in each section lets you cycle forward or backward through the settings.
GETTING THERE FROM HEREThe 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.
CURE FOR THE JITTERSOne digital audio recording aspect that never gets enough attention is the need for sampling-rate synchronization within a digital network. To reduce clicks, pops, and jitter distortion when using multiple digital devices, you must sometimes lock the sampling-rate timing to a single master-clock signal (so devices' conversion states occur simultaneously).
The SRC9624 can lock to an external source through a BNC word-clock connection, through an AES11 port that receives sync data from an XLR cable link, or through a standard AES digital transmission line (the audio information is stripped out at the box). The unit can also generate a master word-clock signal at any of its five internal clock rates, and can resynchronize a jittery input signal that has introduced timing errors (which can cause the audio signal to degrade and sound fuzzy) to any of these rates.
INSIDE CONNECTIONSUsing my M Audio Delta 1010 interface, I recorded a 24-bit, 96 kHz test session with vocals, flute, and percussion. I then transferred the recorded file to my 16-bit, 44.1 kHz DAT recorder and experienced no downsampling hitches. Next I upsampled and downsampled sounds between several devices at various rates, using all three formats and various master-clock configurations. Again, I had no problems. Data paths A and B were indeed independent and passed data without interaction, except that changing any switch setting on one caused the other to momentarily glitch and mute. I just had to remember to leave the front panel settings alone when an audio signal was passing through the unit.
The input connections for the different formats are completely separate and selectable from the front panel; this simple feature lets you use the SRC9624 as a digital patch bay. For example, you could plug a DAT into AES port A, a workstation into S/PDIF port A, and a CD player with optical S/PDIF into port B, then route signals between them (or route a single input to several devices) by just flipping the front-panel switches. The input status LEDs light up only when data is present at the input, a seemingly minor feature that saves time when you can't figure out why you can't get audio into your DAT machine.
I LOVE LUCIDThe SRC9624 is perfect for music, video, and broadcast production houses, where you never know what digital format or sample rate will cross your path. It also saves time and labor. Changing between sample rates, routing between digital devices, and distributing data for making duplicates is just a flick of a switch away.