Audio Application Notes
iPad Streams High-Resolution Audio to Benchmark DAC1
iPad Music Server
A simple USB adapter made by Apple can enable the iPad to connect directly to a Benchmark DAC1.
Using this adapter, the iPad can transparently stream high-resolution digital audio to the USB input of Benchmark converters. Once this connection is established, it is also possible to wirelessly stream a 96-kHz, 24-bit audio to the iPad and out to the DAC without losing sonic quality.
This application note explains the simple set-up and shows proof of performance.
UltraLockDDS™ Clock System
UltraLockDDS™
- A Low-Jitter Direct-Digital-Synthesis Clock System
The ADC16 is equipped with Benchmark’s new UltraLockDDS™ clock system. This 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.
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.
The Unique Evils of Digital Audio and How to Defeat Them
Eliminating Digital Artifacts
- Is digital audio fundamentally flawed?
- Have we followed the wrong path since the introduction of the CD in 1982?
- Should we go back to analog audio systems?
- Has anything improved since 1982?
- How good can digital audio get?
To answer these questions, we will look at the root causes of distortion and noise in digital systems. We will examine how these differ from the distortion and noise in analog systems. Most importantly, we will look at the effectiveness of today’s solutions to these digital problems.
DAC1 Solves Jitter Problems in CD Players with Pitch Control
Benchmark DAC Removes Jitter Caused by Pitch-Control
Variable-pitch features add versatility to CD players. Unfortunately, these features usually create jitter problems. Benchmark’s UltraLock™ jitter-attenuation system provides a unique solution that is fully compatible with variable-pitch transports.
Asynchronous Upsampling to 110 kHz
The Advantages of Asynchronous Upsampling D/A Converters
Benchmark DAC1 converters use upsampling techniques to improve the quality of the digital to analog conversion. Benchmark’s choice of 110 kHz is slightly unorthodox. It may seem more logical to upsample by 2X or 4X and convert at standard sample rates such as 88.2 kHz, 96 kHz, 176.4 kHz or even 192 kHz. Intuition may suggest that integer ratios would produce the best results. Intuition may also suggest that higher is better, and therefore 192 kHz would be the “best” choice for an output sample rate. Unfortunately, intuition often leads us down the wrong path if it is not balanced with reason and scientific analysis. Benchmark’s analysis and testing has shown that 110 kHz offers advantages over the choices that seem more reasonable.
This paper is a short summary of the decisions that led to our choice of the 110 kHz sampling rate.
Volume Control Technologies
Fix the Weakest Link in the Audio Chain!
A playback system's volume control is often one of the weakest links in the audio chain. This is especially true when remote control is required.
Benchmark’s HDR-VC™ (High Dynamic Range Volume Control), combines the best features of two distinct volume control methods while adding remote volume control.
- How does a volume control degrade the sound?
- What are the different volume control methods?
- Are some sonically superior, and why?
Jitter and its Effects
By John Siau and Allen H. Burdick
This paper addresses these questions:
- How and where do I measure jitter, and how do I eliminate it?
- How does sample clock jitter relate to interface jitter measured at digital output connectors?
- How can we accurately measure jitter?
- Why does sample clock jitter have to be so low?
Word-Length Reduction of Digital Audio
Benchmark NN™ and NS™ Word Length Reduction Systems
The AD2404-96 and the SONIC AD2K+ are equipped with two state-of-the-art world-length reduction systems: The Benchmark NN™ (Near Nyquist) system, and the Benchmark NS™ (Noise Shaped) system. Unlike most competitive systems, the Benchmark NS™ system is based upon the most current psycho-acoustic models. Furthermore, both Benchmark systems are unique in that they were optimized while factoring in the noise contribution of the recording environment.
Aspects of Sampling, Oversampling, Quantisation, Dither and Noise-Shaping, as Applied to Digital Audio
By Christopher Hicks
"The aim of this article is to dispel as many of the myths surrounding the conversion of audio signals to the digital domain, and back to the analogue domain, as possible, without the aid of mathematics and (much more difficult) without the aid of diagrams."
Copyright, Christopher Hicks, November 1994. V1.11