Simple Audio Effects¶

Three foundational audio effects built on delay lines.

Delay / echo¶

A circular buffer with feedback creates repeating echoes that decay geometrically:

\[\begin{split}s[n] &= x[n] + \text{feedback} \cdot s[n - D] \\ y[n] &= \text{dry} \cdot x[n] + \text{wet} \cdot s[n - D]\end{split}\]

import pyminidsp as md

signal = md.sine_wave(44100, freq=440.0, sample_rate=44100.0)
echoed = md.delay_echo(signal, delay_samples=4410,
                        feedback=0.5, dry=1.0, wet=0.5)

Before:

After:

Tremolo¶

Amplitude modulation by a sinusoidal LFO. The gain oscillates between 1 - depth and 1:

\[g[n] = (1 - d) + d \cdot \frac{1 + \sin(2\pi f_\text{LFO} n / f_s)}{2}\]

tremmed = md.tremolo(signal, rate_hz=5.0, depth=0.5, sample_rate=44100.0)

Before:

After:

Comb-filter reverb¶

Feeds delayed output back into itself, creating closely-spaced echoes that simulate reverberation:

\[\begin{split}c[n] &= x[n] + \text{feedback} \cdot c[n - D] \\ y[n] &= \text{dry} \cdot x[n] + \text{wet} \cdot c[n]\end{split}\]

reverbed = md.comb_reverb(signal, delay_samples=1000,
                           feedback=0.5, dry=1.0, wet=0.3)

Before:

After:

Verification tips¶

Impulse response: feed an impulse through each effect. Echoes should decay predictably based on the feedback value.
Parameter extremes: depth=0 for tremolo should return the original signal unchanged.
Feedback = 0: all effects should produce a single delayed copy (no ringing).

md.shutdown()