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The USB Converter You've Been Waiting For
There are numerous USB converters on the market, and Bryston typically took its time before releasing one of its own. The Bryston BUC-1 USB Converter delivers the level of uncompromising performance that you would expect from a company that has built its reputation on only producing the highest level components. The BUC-1 has been definitely worth the wait.
The Bryston USB Converter provides a high resolution, ultra low jitter digital audio signal interface with your computer utilizing a single USB cable. The BUC-1 allows for native 24-bit resolution at sampling rates up to 192 kHz. It uses low phase noise clocks to run as the master audio clock, resulting in extraordinarily low jitter output. Digital outputs include AES/EBU, BNC, and coaxial. High quality output transformers isolate the output signal from any computer noise.
Ultra-Low Amounts of Jitter
The goal of any quality USB converter is to convey the exact bits in the audio signal, with the least amount of jitter. Most USB converters are capable of delivering the correct bits. However, the timing is a different matter. Timing errors in the signal can come from a number of different sources, including noisy power supplies or clocks, timing errors already present on the audio signal being encoded, and noise in the transmission line.
Most crucially, the Bryston USB Converter controls the master timing of the audio system. So, instead of your computer running the master clock, and the audio device slaving to this, the main system clock is in the Bryston USB Converter, and the rest of the system slaves to it.
The last feature, which is frequently referred to by the technical name "asynchronous" (as opposed to "isochronous"), is the key to obtaining ultra-low jitter on USB devices. With asynchronous USB receivers, the jitter is essentially limited only by the clocks on the audio device, plus any very small timing errors from additional logic gates that the clock signal must travel through.
Proprietary High Quality Power Supply
Critical to any high-end audio design is the power supply. Most USB type adapters are powered through the USB bus connection in the computer. The power coming from the computer is supplied at 5 volts, and is typically not terribly clean, due to noise in the computer and other attached peripherals, such as hard drives. The BUC-1 employs a proprietary high quality Bryston power supply with ultra-low noise linear power regulation and clean power rails for the internal circuitry.
Filtering and Regulation for Exceptionally Clean Power
In order to supply clean power to the on-board circuitry, the Bryston uses a combination of power supply filtering and a newly released power down regulator. Power coming into the device is first PI filtered (CLC), which gives a two-pole attenuation for noise above roughly 3 kHz. This works to eliminate high frequency noise, which down-regulators are typically not as good at rejecting. This filtered signal, which is slightly less than 5V (due to resistive elements in the passive filter), is down-regulated to 3.3V for the digital electronics, and a separate 3V line for the clocks.