ECE 3551ECE 3551Microcomputer Microcomputer

Systems ISystems IAudio EffectsAudio Effects

By: Saeed MalkyBy: Saeed Malky

Instructor: Dr. KepuskaInstructor: Dr. Kepuska

Project GoalsProject Goals

Effects Implemented:Effects Implemented:• ReverberationReverberation• EchoEcho• VibratoVibrato• ChorusChorus• FlangingFlanging• Increasing and Decreasing the VolumeIncreasing and Decreasing the Volume

System OperationSystem Operation

PF8 is used to toggle between PF8 is used to toggle between Reverberation, Echo and vibrato.Reverberation, Echo and vibrato.

PF9 is used to toggle between Chorus PF9 is used to toggle between Chorus and Flangingand Flanging

PF10 is used to increase the volume.PF10 is used to increase the volume. PF11 is used to decrease the volume.PF11 is used to decrease the volume.

System FeedbackSystem Feedback LED4(on) is used to indicate ReverberationLED4(on) is used to indicate Reverberation LED5(on) is used to indicate echoLED5(on) is used to indicate echo LED4&5(on) is used to indicate VibratoLED4&5(on) is used to indicate Vibrato LED6(on) is used to indicate chorusLED6(on) is used to indicate chorus LED7(on) is used to indicate FlangingLED7(on) is used to indicate Flanging LED4>>led9 increase everytime you increase LED4>>led9 increase everytime you increase

the volume.the volume. LED9>>led4 decrease everytime you decrease LED9>>led4 decrease everytime you decrease

the volume.the volume.

ReverberationReverberation

A rudimentary reverb can be created by adding A rudimentary reverb can be created by adding an infinite number of delays.an infinite number of delays.

The difference equation used may be reduced to The difference equation used may be reduced to the form:the form:

y[n] = x[n] + y[n] = x[n] + ααy[n-D]y[n-D]

EchoEcho

The echo effect may be created by The echo effect may be created by delaying the input signal by delaying the input signal by approximately 15-30ms. The delayed approximately 15-30ms. The delayed version of the input signal is sent as an version of the input signal is sent as an output to one channel and the original output to one channel and the original signal sent as an output to a different signal sent as an output to a different channelchannel

This gives the impression of a stereo This gives the impression of a stereo effect using a mono source.effect using a mono source.

The above flow diagram is used to The above flow diagram is used to implement the echo effectimplement the echo effect

Circular BufferingCircular Buffering The structure The structure shown was used for shown was used for many of the time many of the time varying sound varying sound effects.effects.

Each input is stored Each input is stored in to the delay line in to the delay line buffer while the buffer while the moving output tap moving output tap is obtained from a is obtained from a different location in different location in the buffer rotating the buffer rotating from the tap center.from the tap center.

ChorusChorus The chorus effect “thickens” sound. It The chorus effect “thickens” sound. It

may be used to duplicate the effect of may be used to duplicate the effect of many instruments being played many instruments being played simultaneously.simultaneously.

This effect was created with a variable This effect was created with a variable delay line rotating about a tap center and delay line rotating about a tap center and adding the time varying delayed result adding the time varying delayed result together with the original signal.together with the original signal.

The varying time delay was updated The varying time delay was updated using the equation:using the equation:

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

FlangingFlanging

Flanging was implemented in a similar Flanging was implemented in a similar manner to the chorus effect. The only manner to the chorus effect. The only difference is that the depth of the signal difference is that the depth of the signal is lower around 0.25 to 25ms.is lower around 0.25 to 25ms.

The effect which is created is similar to The effect which is created is similar to that of a “swooshing” jet engine.that of a “swooshing” jet engine.

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

VibratoVibrato The vibrato effect is implemented very The vibrato effect is implemented very

similarly to the chorus effect with the only similarly to the chorus effect with the only notable change being that the original notable change being that the original input signal is not combined with the time input signal is not combined with the time varying signal.varying signal.

By varying the depth of the signal with By varying the depth of the signal with enough modulation, a pitch oscillation is enough modulation, a pitch oscillation is produced giving rise to the vibrato effect.produced giving rise to the vibrato effect.

The vibrato effect The vibrato effect uses a sine or cosine uses a sine or cosine wavetable to wavetable to generate a variable generate a variable delay rotating around delay rotating around a tap center.a tap center.

Since the original Since the original signal is not required signal is not required in the output, the in the output, the difference equation difference equation (shown to the left) is (shown to the left) is used.used.

ReferencesReferences

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