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Subject: CMX608, CMX618 and CMX638 - (PE0002 and EV6180 EvKits)
Optimising the speech quality using both manual and autonomous techniques to set the input gain
Vector quantisation, as a compression method, is sensitive to distortion products in the input
signal and the perceived voice quality of the decoded signal rapidly deteriorates as the input
signal level begins to clip when the ADC runs out headroom.
The input level may be managed using a number of techniques depending on the application.
This application note explores some of these techniques and how they might be applied to obtain best performance from the Vocoder.
Demonstration scripts for use with this application note are available from the scripts area
of this website:
[PE0002 and EV6180 script files]
[application note link]
Publication: AN/2WR/CMX6x8gain_set/1 August 2008
Subject: CMX608, CMX618 and CMX638 Voice Storage and Retrieval - using on-chip voice-data storage
This application note describes a Voice Storage and Retrieve (VSR) function that can be uploaded to the CMX608, CMX618 and CMX638 RALCWI Vocoder ICs.
The VSR function is supplied as a Function ImageTM that can be stored in the host
microcontroller's flash memory for uploading into the RALCWI Vocoder following device
initialisation.
This Function ImageTM is available from the CMX6x8 area of the
'MyCML Portal'.
Please note that you need to be authorised to enter the MyCML Technical Portal. Please contact
your local CML distributor or representative.
PE0002 Scripts are provided for easy evaluation using the RALCWI Vocoder evaluation kits, EV6180 or EV6380, and the PE0002 Interface Card.
[application note link]Subject: CMX618 Voice Storage and Retrieval - using external voice-data storage
The ability to store and retrieve voice is used in a wide range of applications. Good voice quality and reasonable memory requirements are key to the successful implementation of this function. Unfortunately, these two requirements are often mutually exclusive.
The CMX618 RALCWI Vocoder IC from CML Microcircuits provides near toll-quality speech from bit rates as low as 2050bps. This innovative device allows longer recording times for a given sized memory device than other voice coding schemes, while providing good voice quality.
The purpose of this application note is to illustrate how the CMX618 can be configured to perform voice storage and retrieval. This information is not intended to be a reference design, but is intended to act as a “seed” to accelerate development of CMX618-based designs.