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Chorus Effects:
Chorus Effect with Feedback
Chorusing effect simulating 2 voices/musical instruments (SPORT1 Rx ISR count & update method - delay calculation determined by a counter incremented in the serial port's audio processing routine).
Stereo Chorus with Feedback
Stereo chorusing effect simulating 3 voices/musical instruments (SPORT1 Rx ISR count & update method - delay calculation determined by a counter incremented in the serial port's audio processing routine).
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Download file
(zip, 143,429 bytes)
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DeTune Effects:
Two Voice - ISR Update Method
Pitch Shift Effect Simulating 2 Voices Slightly Out Of Pitch (ISR Update Method - delay calculation determined by a SPORT0 rx ISR counter).
Two Voice - Timer Update Method
Pitch Shift Effect Simulating 2 Voices Slightly Out Of Pitch (Timer0 Update Method - delay calculation determined by the on-chip programmable timer).
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Download file
(zip, 197,272 bytes)
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Digital Delay Effects:
ADT & Slapback
Slapback ('Doubling') Effect (also called Mono Automatic Double Tracking). The effect is created by adding a delayed signal together with the original, where a single input source is mixed with the delay, and the result is sent to both output channels.
Automatic Double Tracking
Stereo Automatic Double Tracking (Stereo Doubling) - "Concert Announcer Simulation." This effect is set up to playback the original "dry" signal in one stereo channel and the delayed signal in the other channel. This creates the impression of a stereo effect using a single mono source.
Digital Delay - Single Reflection
A Single digital delay consists of delaying an input signal using a delay-line, and adding the delayed signal back to the original. An FIR comb filter results.
Multiple Delay
Multiple digital delays can be created by delaying an input signal using multiple delay-lines, and adding the delayed signals back to the original.
Multi-Tap Delay
Multiple delayed values of an input signal can be combined easily to produce multiple reflections of the input. This can be done by having multiple taps pointing to different previous inputs stored into the delay line, or by having separate memory buffers at different sizes where input samples are stored.
Reverb Delay
A reverberating delay consists of adding delayed replicas of an input together with the direct input signal. In this implementation, the direct signal is combined with a gain controlled IIR comb filter.
Slapback Delay
Slapback ('Doubling') Effect (also called Mono Automatic Double Tracking). The effect is created by adding a delayed signal together with the original, where a single input source is mixed with the delay, and the result is sent to both output channels.
Stereo Delay
Stereo delay effects can be implemented by coupling the left and right channels. The left and right channels are coupled by introducing cross-feedback coefficients, so that the delayed output of one channel is fed into the input of the other channel.
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Download file
(zip, 327,696 bytes)
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Digital Reverberation Effects
Griesinger's Plate Reverb
Digital Plate-Class Reverberation Audio Effect which works well for single instruments such as a guitar, keyboard, violin, etc.
Griesinger's Plate Reverb w delay modulation
To improve reverberation responses for drums or other impulse signals, linear interpolation is used to slowly modulate the nominal tap point for two of the tank diffusers. Works well on vocals and drums, but not recommended for guitars/keyboards because of perceived vibrato from delay modulation.
Moorer's Reverb
This effect uses a low pass comb filter for each reverb stage to enlarge the density of the response. The technique involves 6 parallel comb filters with a low pass output, summing their outputs and then sending the summed result to an all pass filter before producing the final result.
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Download file
(zip, 534,786 bytes)
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Reverb Building Blocks ToolKit
All Pass - Canonical
IIR comb filters tend to magnify input signal frequencies near comb filter peak frequencies. All pass filters can be used to prevent this 'coloration' of the input since it has a relatively flat magnitude response for all frequencies.
All Pass - Transpose
Similar to the Canonical All pass filter except the filter structure is slightly different.
IIR Comb Filter
Comb filters are used for noise reduction of periodic signals, signal enhancement, averaging signals, and are inherent in digital audio effects such as delays, chorus and flange effects. Comb filters work by adding a signal with a delayed and scaled version of the same signal.
Low Pass IIR Comb Filter
The use of a low pass comb filter in reverb algorithms causes each echo to spread out, or smear. This results in a much more diffused, mellowed response, and also more closely replicates the fact that higher frequencies diminish faster than lower frequencies in reverberant spaces.
Stereo All pass Filter
Same as the previously described all pass filter, except this one works in stereo.
Stereo IIR Comb Filter
Same as the previously described IIR comb filter, except this one works in stereo.
Schroeder's Reverb
This effect uses four IIR comb filters in parallel, with their output results added together, followed by 2 cascaded all pass filters stages. Also, Schroeder's Reverb keeps the high reflections ringing longer since plain IIR comb filters are used.
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Download file
(zip, 534,786 bytes)
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Dynamic Range Control Effects
Compander
Combination of a compressor and expander. The peaks signal levels above the upper threshold are compressed, while lower level signals above the lower threshold are expanded.
Compressor
Keeps the level of the signal within a specific dynamic range, using a technique called 'gain reduction'. The objective of a compressor is to make sure that the signal level does not go beyond a desired level, thus restricting the dynamic range.
Expander
Opposite of a compressor, with opposite input/output ratios. This effect is often used to recover the full dynamic range of a compresses signal. Also useful for reducing noise in tape recording and wireless systems by increasing the level of the audio signal relative to low-level noise beyond a low threshold.
Noise Gate - Downward Expander
Reduces the amount of gain below a certain threshold to reduce or eliminate noise produced when no audio signal is present, while still allowing the signal to pass through. This is useful after processing multiple audio effects that can introduce noise above the noise floor of the AD1819a DACs.
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Download file
(zip, 165,634 bytes)
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Flanger
Flanger with Feedback
Flanging consists of modulating a delayed replica of an input by a few milliseconds and adding this delayed signal together with the input, which will then cause phase shifting and spreading of the audio signal as a result of comb filtering. The delay is modulated using a low frequency sinusoid. The effect works best on drums, guitars, keyboards, and some vocals.
Stereo Flanger
Same as previously described Flanger, but works in stereo.
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Download file
(zip, 127,308 bytes)
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Guitar Distortion Simulation
This routine will square the input and cause it to clip at positive and negative full scale to simulate the effect of saturating an op amp or overdriving audio amplifier speakers (The Hendrix Effect).
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Download file
(zip, 45,510 bytes)
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Phaser Effect
This effect is produced by passing an audio signal through a narrow notch filter and combining a proportion of the filter's output with the direct sound. The frequency of the notch is then varied using a low-frequency oscillator.
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Download file
(zip, 65,471 bytes)
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Pitch Shifter
1 Single Pitch Shift
An interesting and commonly used effect is changing the pitch of an instrument or voice. The pitch shifter requires using a sawtooth/ramp wavetable to achieve a 'linear' process of dropping and adding samples in playback from an input buffer.
2 Part Harmony w CrossFade
This version crossfades between two buffers to prevent 'clicks & pops' of input and output pointer wraparounds. A slight audible modulation occurs at higher pitch shift values.
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Download file
(zip, 251,580 bytes)
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Rotating Speaker Emulation
This effect consists of a combination of the tremolo and vibrato effects, combined a low-pass filter with a variable cutoff frequency. The resulting sound heard by the ears is a cyclical increase/decrease in volume, a doppler effect from the speaker rotating, and a cyclical drop in high frequencies whenever the speaker is facing away from the listener.
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Download file
(zip, 62,475 bytes)
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Tremolo
ISR Count Method
Tremolo consists of panning the output result between the left and right output stereo channels at a slow periodic rate. This is achieved multiplying the amplitude of the incoming signal with a low frequency sinusoid. The stereo example pans the output to the left speaker for +sine values and pans the output to the right speaker for -sine values.
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Download file
(zip, 60,844 bytes)
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Vibrato
Vibrato ISR_Count_Method
This effect is achieved by evenly modulating the pitch of the signal. It is similar to a guitarist moving the 'whammy' bar, or a violinist creating vibrato with cyclical movement of the playing hand.
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Download file
(zip, 73,089 bytes)
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WaveMusic Demo
This routine generates a song using tones generated from a sine function approximation routine.
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Download file
(zip, 40,606 bytes)
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Digital Filters
FIR Filter - High Pass & Low Pass
Standard Finite Impulse Response Filter.
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Download file
(zip, 41,809 bytes)
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