Next: 4 Advanced topics Up: 3 Using MIDAS Digital Previous: 3.6 Playing streams

# 3.7 Using echo effects

The MIDAS Digital Audio System Echo Effects Engine can be used to add different echo and reverb effects to the sound output. These effects can range from simple echoes and filtering effects to heavy hall reverbs and stereo enhancements. This section describes how the echo effects are used

## 3.7.1 Adding echo effects

Echo effects are added to the sound output with MIDASaddEchoEffect. It takes as an argument a pointer to a filled MIDASechoSet structure (described below), and returns and echo handle that can then be used to refer to the effect. The echo set structure is not used after MIDASaddEchoEffect returns, and may be deallocated. Any number of echo effects can be active simultaneously.

After the echo effect is no longer wanted, it can be removed from the output with MIDASremoveEchoEffect. Note that modifying the MIDASechoSet structure of an echo effect that is already being used has no effect.

## 3.7.2 The echo effect structure

A MIDAS Digital Audio System echo effect is described by a MIDASechoSet structure. The echo set contains three common fields plus one or more echoes. The feedback field controls the amount of feedback in the echo set, gain the echo effect total gain, and numEchoes simply the number of echoes in the echo set. See the MIDASechoSet description in the API Reference for more details.

The echoes of an echo set are described by an array of MIDASecho structures. Each echo has fields that describe its delay, gain, filtering and channel reverse status. The delay of an echo controls how far back from the echo effect delay line the data for the echo is taken -- the greater the delay, the longer the echo is. Gain controls the strength of the echo, the echo data is essentially multiplied by the gain. Each echo can optionally be low-pass or high-pass filtered, in a system with more than a couple of echoes, low-pass filtering can reduce the build-up of high-frequency noise. Finally, the left and right channels of the echo can be reversed, producing an interesting stereo effect in some cases.

Next: 4 Advanced topics Up: 3 Using MIDAS Digital Previous: 3.6 Playing streams