Digital Speech Processing
Test Bed Development & System Evaluation
The evaluation of single or multiple real-time voice coders requires an infrastructure in order to easily and consistently implement the test methods required for a successful evaluation.
- A test bed for voice communication system technology centers around a common interface device that will have at it's most basic hardware component level the following modules:
- 1. A "Front-end" that accepts analog audio signals, digitizes them and presents them to the coder analyzer inputs.
- 2. A switch to select among various coders or other reference systems.
- 3. A method to access and manipulate the coded bitstreams.
- 4. A "Back-end" that outputs analog processed speech from the coder synthesizer outputs.
Other hardware features may include a common clock, digital audio I/O for file-to-file processing or a common platform for the coders themselves.
A Channel simulator is often inserted between coder analyzers and synthesizers. It allows the introduction of channel simulations and also affords the opportunity to examine the coded bitstreams and determine or enforce any protocols designed into the test plan such as bit rate, frame size, start of frame indication, frame sync methods, etc.
A test bed also requires devices for high quality audio playback and recording, such as DAT decks or professional hard disk systems. For tests requiring live users such as communicability, facilities must include user stations in areas with consistent and known acoustical backgrounds, such as anechoic chambers. Communicators must then be outfitted with transducers that would are specified for the system or be resident to the environment required for the given scenario.