CSR showcases apt-X Live audio CODEC demonstrator for low-power, spectrum-efficient Digital Wireless Microphone systems

Digital wireless microphone systems offer numerous performance advantages and end-user benefits over conventional analogue designs. An important attraction is their potential to offer more efficient use of the radio frequency spectrum for a given audio quality. Spectrum-efficiency is fast-becoming a make-or-break design issue owing to ongoing moves by government authorities to downsize the radio frequency band allocations for the legal operation of wireless microphones in the US and elsewhere. Key to microphone designs achieving this spectrum efficiency is the use of low-latency audio compression technology as an essential sub-system in the signal processing chain.

CSR’s apt-X Live CODEC is specifically designed for the exceptional requirements of digital wireless microphones. The patented architecture provide generous audio data rate reduction and an enhanced degree of error tolerance, all with extremely low latency.

This apt-X Live evaluation platform comprises separate digital radio transmitter and receiver modules, and is designed to demonstrate how the all-important low-latency audio CODEC subsystem within a typical digital wireless microphone system can be successfully implemented using CSR’s apt-X Live.

In operation, the programmable DSP-based digital radio transmitter module takes a mono channel audio input (16-bit resolution, sampled at 48kHz) and compresses this in real-time using the apt-X Live algorithm running at 2.5 bits per PCM sample to produce a compressed bitstream at 120kbits/sec. This bitstream is digitally modulated using FSK onto an 868MHz RF carrier, and transmitted over the air to a similar DSP-based receiver module that demodulates the bitstream, and decompresses the data to reproduce the original PCM audio signal.

The apt-X Live audio CODEC can deliver a single channel of 24bit, 48kHz audio in 120kbps with a codec latency of less than 1.9ms.The framework of apt-X Live audio coding will provide a higher resilience to random bit errors. Additional techniques employed within apt-X Live also will reduce the significance of these errors and the magnitude of the audible effect on certain signals.

Chris Havell, Director of Audio Marketing, CSR commented: “Our evaluation platform helps to prove the CSR low-latency apt-X Live audio CODEC’s ability to satisfy key design criteria for deployment in digital wireless microphone systems. We expect audio system designers will be impressed with the audio bandwidth, dynamic range and end-to-end audio latency of this apt-X Live demonstrator. These are the fundamental parameters which determine overall performance of digital wireless microphone systems.”