By John Siau
When Benchmark unveiled UltraLock™, it caused quite a stir. Benchmark claimed that this proprietary clock-syncing system made their converters immune to jitter. UltraLock™ keeps jitter-induced distortion at or below -135 dB FS (well below audibility). Of course, the audio community was skeptical; they set out to prove (or disprove) Benchmark’s claims. Since then, several journalists, end-users, and manufacturers of audio test-equipment have verified Benchmark’s claim of jitter-immunity.
However, there was still room for improvement. There is an asynchronous sample rate conversion (ASRC) process in UltraLock™ that adds about 1 millisecond of latency. This latency is usually only of concern when musicians are monitoring themselves real-time, post-converter. Even in this case, 1 millisecond of latency is hardly noticeable; it is roughly equivalent to having the instrument 1 foot further away. Nevertheless, it can contribute to a system-wide latency problem.
When designing the ADC16, Benchmark decided to revisit its clock-management solution, to reduce latency. The technology that Benchmark developed during this quest is called UltraLockDDS™.
Benchmark’s new UltraLockDDS™ clock system utilizes the latest low-jitter clock technology developed for high-frequency RF communications systems. The master oscillator is a low phase-noise, temperature-compensated, fixed-frequency crystal oscillator with a +/- 2 PPM frequency accuracy. This oscillator drives a 500 MHz Direct Digital Synthesis (DDS) system that generates a 3072 x WC system clock. This high-frequency clock is divided and distributed directly to the A/D converters using a high-speed PECL clock distribution chip. Each of the 8 converters is driven directly through a dedicated, matched-impedance transmission line.
Jitter attenuation is achieved with digital filters in a custom FPGA that controls the DDS system. All jitter-induced distortion artifacts are well below audibility under all operating conditions. Jitter-induced distortion is always at least 135 dB below the level of the music. The jitter-performance of UltraLockDDS™ meets or exceeds the performance of Benchmark’s UltraLock™ system, but does not use an ASRC DSP process. The elimination of the ASRC processing significantly reduces system lateancy and provides the most direct path from the A/D to the digital interface.
If an audio system is composed of multiple components, we may have detailed specifications for each component, but we will not know the performance of the combined system without doing some calculations. You may have questions such as these:
Use Benchmark's online audio calculators to find answers!
For example, if we know the output power of an amplifier, as well as the sensitivity and impedance of our loudspeakers, we can calculate the maximum sound pressure level that our system can produce.
This application note provides interactive examples that help to answer the questions listed above.
We have added an "Audio Calculators" section to our webpage. Click "Calculators" on the top menu to see more like these:
Secrets contributor Sumit Chawla recently caught up with Benchmark’s VP and Chief Designer, John Siau to get a little more in-depth on several subjects.
Q: "Benchmark is one of the few companies that publishes an extensive set of measurements, but you also balance that with subjective testing. Can you talk about the equipment, the listening room, and the process for subjective testing?"
Q: "Was there ever a time where you learned something from a subjective test that was not captured by measurements?"
Q: "You conducted some listening tests to determine whether distortion in the “First Watt” was audible. What test material did you use for this, and what did you find?"
Q: "The AHB2 amplifier incorporates THX Audio Achromatic Amplifier technology. When and how did the partnership with THX come about?"
Q: "Linear power supplies have been and remain quite popular in high-end devices. You favor switch-mode power supplies. When and why did you make this switch?"
... and more!