Music delivery systems are rapidly changing. The days of a CD changer and a huge library of CDs is quickly being replaced by a computer with the content residing on a large harddrive.
Unfortunately, the internal soundcards in most computers are not nearly good enough for the demands of high quality audio.
USB Audio Class 2 has become the interface of choice for extracting the digital content from the music server computer to a target DAC or headphone amplifier. This is a relatively recent development. Although USB audio has been around since the early days of USB, it was basically a 48k, 16 bit stereo interface (USB Audio Class 1.1). USB Audio Class 2 can support multiple channels at high sample rate and full bit depth. It uses an external clock from the USB client that helps insure minimal jitter at the target device.
The leader in USB audio class 2 chip solutions is XMOS. Danville Signal is a third party partner with XMOS. We have utilized and extended their technology in several ways, primarily by combining their chips with Analog Devices' SHARC DSPs. This allows the XMOS device to concentrate on communications while the DSP to manages signal processing and control.
An audio class driver is mostly concerned with streaming audio data at various sample rates and bit depth. It has limited control, such as volume up and down. Danville has extended the control capability of our XMOS targets by appending a HID interface into the XMOS code. This allows us to download code or instructions to the DSP or interface to a graphical design and tuning interface such as DSP Concepts' Audio Weaver. We supply a Window DLL so that custom programs can be easily created to take advantage of these features without the need to be an XMOS programmer.
There is native USB Audio Class 2 support for Apple and Linux. Microsoft has not opted to provide similar support with their operating systems. This may be because USB Audio Class 2 places demands on the computer that not all PCs can support. We have driver support for Microsoft Windows (XP, 7 & 8). We provide these drivers with our general purpose dspblok modules such as our dspblok 21479u8a and with our more dedicated targets such as our wireless audio transmitters.
If you are considering your own design, we suggest you consider our dspblok 21479u8a. This module combines an XMOS XS1-U8A processor with an Analog Devices ADSP-21479 DSP. We use this module in many of our turnkey OEM audio products. With the dspblok, you don't need to program the XMOS device at all (XMOS programming is tricky). You also get Windows driver support. If you are interested in a more custom solution, we can provide a complete hardware and software package with optional graphical design and tuning capability. Check out the dspblok 21479u8a page for more information.
XMOS-SHARC Audio Class 2 Solution