Time Based Effects

1. Time Based Effects

2. How they work • take a copy of the audio (or many copies • play it back slightly later than the original • change the playback speed of the copy and mix it with the original • Mostly digital

3. Different Types of Time-Based effects • Delay • Reverb • Chorusing • Phasing • Flanging

4. Delay • A copy of the input signal is recorded, stored, and played back after a period of time. • Simulates reflections or an echo • Multi-tap • Early analog delays used tape loops • Digital delay uses a “sample-and-hold” design

5. Reverb • In nature: a series of delayed and attenuated reflections • Reverb simulates the sound of a natural space • Early analog reverbs included bathrooms, plates, springs, and chambers • Digital reverbs can use delay algorithms or convolution

6. Chorus/Unison • When two of the same type of instrument play the same note, there are slight differences in pitch and timbre • Your brain fuses this into one sound • e.g. a violin section • Electronic chorus effect plays a copy of the original signal which is slightly detuned and/or delayed

7. Phasing • Uses an “all-pass” filter to change the phase relationship between high and low frequency components • This is mixed in with the original signal and phase cancellation occurs at different frequencies • Produces a “sweeping” effect

8. Flanging • Flanger is similar to phaser except that a delay is used • This delay is constantly changing • Has a “sweeping” effect - sort of like a jet engine

9. Common Controls • Wet/Dry - controls the mix of the effected signal to the original uneffected signal • Low pass filter - removes high frequency components from the original signal • Delay - sets the amount of time before the delayed signal will be played back • Depth/Rate - controls the LFO which modulates the pitch or amplitude of the effected signal • Feedback - sends a certain amount of the effected signal back through the delay line again - multi-tap delay

10. Common reverb controls • Decay - controls how long the reverb will ring • Predelay - sets a delay time before the reverb begins to play back • Diffusion - sets how much “echo” will be present in the reverb

11. Other time-based effects • Pitch shift – shifts the pitch of the sound by speeding up or slowing down playback time (think Chipmunks). • In the digital world, a sample rate conversion can be done to maintain the original tempo or duration • Time stretch/compression – maintains the original pitch while changing the tempo or duration of the sound • Several methods exist; two most prominent are phase vocoder and Time Domain Harmonic Scaling