ECE 3551 Microcomputer Systems I

1. ECE 3551Microcomputer Systems I Audio Effects By: Saeed Malky Instructor: Dr. Kepuska

2. Project Goals • Effects Implemented: • Reverberation • Echo • Vibrato • Chorus • Flanging • Increasing and Decreasing the Volume

3. System Operation • PF8 is used to toggle between Reverberation, Echo and vibrato. • PF9 is used to toggle between Chorus and Flanging • PF10 is used to increase the volume. • PF11 is used to decrease the volume.

4. System Feedback • LED4(on) is used to indicate Reverberation • LED5(on) is used to indicate echo • LED4&5(on) is used to indicate Vibrato • LED6(on) is used to indicate chorus • LED7(on) is used to indicate Flanging • LED4>>led9 increase everytime you increase the volume. • LED9>>led4 decrease everytime you decrease the volume.

5. Reverberation • A rudimentary reverb can be created by adding an infinite number of delays. • The difference equation used may be reduced to the form: • y[n] = x[n] + αy[n-D]

6. Echo • The echo effect may be created by delaying the input signal by approximately 15-30ms. The delayed version of the input signal is sent as an output to one channel and the original signal sent as an output to a different channel • This gives the impression of a stereo effect using a mono source.

7. The above flow diagram is used to implement the echo effect

8. Circular Buffering • The structure shown was used for many of the time varying sound effects. • Each input is stored in to the delay line buffer while the moving output tap is obtained from a different location in the buffer rotating from the tap center.

9. Chorus • The chorus effect “thickens” sound. It may be used to duplicate the effect of many instruments being played simultaneously. • This effect was created with a variable delay line rotating about a tap center and adding the time varying delayed result together with the original signal. • The varying time delay was updated using the equation:

10. The flow diagram shown was used to implement a stereo chorus effect. Two cosine wavetables were used. A time varying delay signal was sent to the right channel output. Another time varying signal combined with the original input signal was sent to the left channel output.

11. Flanging • Flanging was implemented in a similar manner to the chorus effect. The only difference is that the depth of the signal is lower around 0.25 to 25ms. • The effect which is created is similar to that of a “swooshing” jet engine.

12. The flow diagram shown is used to implement the flanging effect. A time varying signal is combined with the original signal and sent to the output resulting in the following difference equation. d[n] is calculated using a similar equation as the chorus effect.

13. Vibrato • The vibrato effect is implemented very similarly to the chorus effect with the only notable change being that the original input signal is not combined with the time varying signal. • By varying the depth of the signal with enough modulation, a pitch oscillation is produced giving rise to the vibrato effect.

14. The vibrato effect uses a sine or cosine wavetable to generate a variable delay rotating around a tap center. • Since the original signal is not required in the output, the difference equation (shown to the left) is used.

15. References http://my.fit.edu/~vkepuska/ece3551/7056820721065L_Audio_Tutorial.pdf