Codec Takes On Spectrum-Efficiency, Audio-Quality Design Challenges

Dec. 8, 2010

A new DSP-based evaluation platform demonstrated by CSR is aimed at its low-latency, high-quality apt-X Live codec. This technology, suited for professional audio applications, helps overcome the spectrum-efficiency and audio-quality challenges involved in digital wireless microphone and in-ear monitoring system design.

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, due to ongoing moves by government authorities to downsize the radio-frequency band allocations for legal operation of wireless microphones in the U.S. and elsewhere. A key factor toward achieving this spectrum efficiency is the use of low-latency audio-compression technology as an essential subsystem in the signal-processing chain.

CSR’s apt-X Live codec is designed for the requirements of digital wireless microphones.  The patented architecture provides significant audio data-rate reduction and an enhanced degree of error tolerance, all with low latency.

The apt-X Live evaluation platform comprises separate digital radio transmitter and receiver modules. It’s designed to demonstrate how the low-latency audio codec subsystem within a typical digital wireless microphone system can be implemented using apt-X Live.

The programmable DSP-based digital radio transmitter module takes a mono channel audio input (16bit resolution, sampled at 48kHz) and compresses it in real-time using the apt-X Live algorithm, running at 2.5bits per PCM sample to produce a compressed bitstream at 120kbps. This bitstream is digitally modulated using FSK onto an 868MHz RF carrier. It’s then 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 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 the audio coding will provide a higher resilience to random bit errors. Additional techniques employed within apt-X Live also reduce the significance of these errors and the magnitude of the audible effect on certain signals.

Sponsored Recommendations


To join the conversation, and become an exclusive member of Electronic Design, create an account today!