The EV6550DHAT builds on the growing Raspberry Pi ecosystem by bringing the advanced features of the CMX655D voice codec to the community.
The CMX655D has been developed for digital voice and sensor applications. It integrates the entire signal chain, from dual matched digital MEMS microphone interfaces to a 1W Class D speaker driver, incorporating decimation, filtering, signal processing and digital gain, supported by an I2S/PCM audio interface and SPI control interface. It represents a true single-chip, ultra-low power solution to adding advanced voice coding/decoding to any application.
In order to make evaluating and developing with the CMX655D as accessible as possible, CML has created the EV6550DHAT. The HAT is compatible with any Raspberry Pi with a 40-pin extended GPIO connector and can be completely powered by the Raspberry Pi, however it also supports an external power source if other HATs or peripherals are being used and limiting the total power available from the host USB interface.
"The Raspberry Pi is the perfect platform to demonstrate the features and capabilities of the CMX655D with little or no development effort," commented David Brooke, Product Manager, CML Microcircuits. "The EV6550DHAT is our first HAT and the entire team has been excited by the prospect of bringing advanced voice codec capability to the Pi."
As well as being HAT-compliant, the EV6550DHAT open source software is accessible via many third-party apps and projects includingGTK3+. GEANIE and GLADE. This means the GUI used to access the EV6550DHAT and all of the features are easily modifiable and accessible to the engineering community.
Features include access to pre-recorded sample files, as well as the ability to record and playback audio files in the .wav format allowing users to play back the pre-recorded samples at different rates and levels, enabling easier comparison between settings and how they influence audio quality. The configurable parameters include sample rate (choose from 8, 16, 32 and 48ksample/s), volume and level (dB).
The GUI allows the audio input gain to be set between -12dB to +3dB, while playback volume can be set between -90dB to 0dB. Muting and 'smoothing' is also supported.