Advanced voice codec capability for Raspberry Pi

13th February 2020
Alex Lynn

CML Microcircuits has announced the EV6550DHAT, a Raspberry Pi Hardware Attached on Top (HAT) compatible evaluation and development board that makes the features and benefits of its CMX655D ultra-low power voice codec available to hobbyists, developers and product manufacturers.

The hugely popular Raspberry Pi is widely recognised as the platform of choice for rapid hardware and software development. The EV6550DHAT builds on this growing ecosystem by bringing the advanced features of the CMX655D voice codec to the Raspberry Pi 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.

To make evaluating and developing with the CMX655D accessible, 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.

As well as being HAT-compliant, the open source software is accessible via many third-party apps and projects including GTK3, Genie and Glade- making the GUI used to access the EV6550DHAT and all its features 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, 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. 

The EV6550DHAT is available now through our distributors.

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