Black Lion Audio Micro Clock MkIII
By Barry Rudolph
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The Micro Clock MkIII simultaneously generates AES11 clock signal out an XLR 110-ohm balanced out and also S/PDIF clock out optical Toslink and 75-ohm unbalanced RCA jacks. It is capable of up to a 384kHz clock frequency out the six BNC output jacks; the AES and RCA S/PDIF go up to 192 kHz; the optical S/PDIF output is good to 96 kHz.
The MkIII steel clam-shell case has an overall DIY build quality, but the inside reveals an Atmel SAM3X/A Flash microcontroller and Silicon Laboratories' Si530/ 531 XO crystal oscillator chips with onboard DSP phase-lock loop circuitry. There are separate Pulse PE-65612NL digital 1:1 isolation transformers for both the AES/EBU and RCA S/PDIF outputs, while a third Pulse T3001NL isolates the 75-ohm BNC clock signal going to the six BNC line drivers.
What Time Is It?
In the nascent days of digital audio, the early (primitive by today's standards) converters had "sketchy" clocks, and there was an immediate sonic improvement when connecting to a low-jitter external clock. But today, modern clock chip sets and crystals have vastly improved in jitter performance and in price, and are used widely even in the least expensive "semi-pro" digital interfaces.
In simple DAW-based recording studios with a single interface, the internal analog-to-digital (A/D) converter generates the clock signal to "clock in" digital audio at a selected sample rate. The performance of the internal clock within a modern converter is the same or better, as it would be when using an external clock source. Most external clocking issues stem from the vagaries of a converter's slave clock signal recovery/locking circuitry, external clock cabling issues caused by excessive cable lengths, and/or lack of proper 75-ohm termination.
However, for more complex digital audio/video systems with multiple digital processors, digital consoles, MADI or Dante interfaces, and multichannel delivery formats, a master clock is necessary. All of the digital components in these large systems must be clocked from one centralized word clock generator using multiple BNC outputs.
Master ClockingSo my first test was to substitute the Micro Clock for the existing multi-thousand dollar master clock in a Euphonix System 5 console I often work on. The console's SC264 computer, AVID MADI interface (to connect to a Pro Tools 11 HDX rig), and two DirectOut Technologies Andiamo MADI AD/DA converters were clocked perfectly from the Black Lion Micro Clock MKIII's BNC outs with no difference in operation at all. (As a side-note, the Micro Clock is not capable of 0.1-percent and 4-percent pull-ups/pull-downs if you require syncing NTSC video to film or to PAL video.)
For recording in Pro Tools 12 HDX at my mix studio, I prefer the sound of my Benchmark Media ADC1 A/D Converter instead of the internal converters in the old Digidesign HD 192 interface, so I have to externally clock the HD 192 using the ADC1. For playback, I rely on Benchmark Media's DAC1 for digital-to-analog conversion with both the ADC1 and DAC1 connected using the HD192's In/Out AES/EBU XLR Enclosure connectors. The ADC1's BNC word clock out is connected to the external clock input of the HD192 using a short, 75-ohm terminated BNC cable. The DAC1 is always clocked from the AES/EBU digital audio signal coming out of the HD 192, and was the only DAC used in all of my listening tests for this review.
I compared 24-bit/44.1 kHz song mixes I did and know well and also recent 32-bit float solo acoustic guitar and grand piano recordings I made at 96 kHz in Pro Tools using the ADC1. I listened to each one separately clocked internally and externally from either the ADC1 or the Black Lion Audio Micro Clock MKIII. It was not intended as a clock shootout or advanced technical treatise; I was just interested to see if I could hear a difference in sound quality.
I would physically switch clock cables and terminations and wait for a few seconds (after Pro Tools pushed a clocking error dialog) and then go into Play. I used my monitors at various loudness levels and used several sets of headphones trying to detect any differences. I looped very short sections to see if I could hear changes in ambience or tonality.
I could hear no difference. There might be differences to some listeners, so I randomly asked other engineers to take a listen, and nobody could hear any change nor could I tell any difference using any particular program style or recording level.
I really wanted to hear a difference, and sometimes I thought I heard differences such as an overall level jump right after changing clocks. This "level jump" was random and not repeatable. If I were still using an old Digidesign 888 interface and Pro Tools 5, I'm sure I would hear an improvement right away.
The Black Lion Audio Micro Clock MkIII is good value in a small package. Costing about one-third as much, it stood in for a much more expensive clock in the Euphonix System 5 studio. If you have to externally master clock multiple digital devices in your studio, the Black Lion Audio Micro Clock MKII is a good bet.
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