When talking to somebody over a long distance on a cell phone, we often experience annoying lags in a conversation. The delay between when the words come out of the talker’s mouth and when the other person hears them may go as high as several hundreds of milliseconds. The delay in this case is mainly caused by the transmission or packet switched networks.
Similarly, signal processing delay may cause the same effects on the listeners. We use the In-Car-Communication(ICC) system as an example.
The In-Car-Communication system can be illustrated by the above sketch. The driver is the talker and the listener is a back-seat passenger. When driving on a highway, the driver will have a difficult time to talk to the passenger over the loud noises that may come from the car chassis, the tire, the road and sometimes even the wind when windows are open. ICC is a system that provides a solution for such situations.
The system consists of a microphone, a speaker and a digital signal processing unit for speech enhancement. The driver’s speech is captured by the microphone installed close to the driver. The microphone captured signal will be heavily corrupted with the above mentioned car noises. ICC applies various needed signal processing techniques to clean up the speech before sends to a speaker located close to the back seat passenger.
Regardless how noisy the environment is in a car, there is always a direct acoustic path between the driver and the passenger. It only takes a few milliseconds for the driver’s speech to reach the back seat passenger through the acoustic path. Therefore, the processing delay by the ICC unit must be restricted to less than 20 milliseconds for conversation to appear natural.
VOCAL technologies low-delay DSP solution is specifically designed for delay-critical applications.