Signal processing
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Signal Processing. Using the effects in Garageband. Signal Processing. Audio signal processing , sometimes referred to as audio processing , is the intentional alteration of auditory signals, or sound, often through an audio effects unit . Filters.

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Signal Processing

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Signal Processing

Using the effects in Garageband

Signal Processing

  • Audio signal processing, sometimes referred to as audio processing, is the intentional alteration of auditory signals, or sound, often through an audio effects unit.


  • An audio filter is a frequency dependent amplifier circuit.

  • Most DAW software will give the user access to filters in an equalizer (EQ)


  • The three most common audio filters are:





  • The three most common audio filters are:

    low-pass – filters out high frequencies

    high-pass – filters out low frequencies

    bandpass– only allows a narrow band of frequencies through








  • A delayis an audio effect which records an input signal to an audio storage medium, and then plays it back after a period of time.

  • The delayed signal may either be played back multiple times, or played back into the recording again, to create the sound of a repeating, decaying echo.


  • Reverb is the persistence and gradual decay of sound in a particular space after the original sound is produced.

  • While a delay effect causes a distinct “echo” shortly after a sound’s production, reverberation is the effect of thousands upon thousands of echoes that occur in quick succession as the sound bounces across surfaces in space.


  • Tremolo is is the variation in amplitude of sound achieved through sub-audio amplitude modulation.

  • In sub-audio amplitude modulation, a modulating wave that is lower than humans can hear is applied to the carrier (the actual sound). This causes a regular “wobbling” of the sound.


  • A chorus effect is achieved by taking an audio signal and mixing it with one or more delayed, pitch-modulated copies of itself.

  • This will make the sound “richer” or “fuller”. Think about how one violin sounds compared to an entire section of violins playing the same melody.


  • A phaserfilters a signal by creating a series of peaks and troughs in the frequency spectrum. The position of the peaks and troughs is typically modulated so that they vary over time, creating a sweeping effect.


  • A flangercreates an identical copy of the original signal, delays it by a small (but gradually changing) amount, and mixes the two together.

  • The result is similar to a phaser, but is slightly more “distorted” and “edgy”.

Distortion / Overdrive

  • A distortion or overdrive effects unit simulates the effect of the same name that is available on guitar and bass amplifiers.

  • The effects unit compresses the original signal until it begins to take on the shape of a square wave. The result is a “gnarly” sound that simulates overdriven analog signals.


  • A bitcrusher effects unit produces a distortion by the reduction of the resolution or bandwidth of digital audio data.

  • This is an effect that essentially lowers the bit depth and sample rate of the digital audio.

Ring Modulation

  • Ring modulationis a signal-processing function in electronics, an implementation of amplitude modulation or frequency mixing, performed by multiplying two signals, where one is typically a sine-wave or another simple waveform.

Compressors / Limiters

  • Dynamic range compression, also called DRC (often seen in DVD and car CD player settings) or simply compression reduces the volume of loud sounds or amplifies quiet sounds by narrowing or "compressing" an audio signal's dynamic range.

  • Compressors are processor intensive and will change the dynamic curve of a signal. Limiters are simpler effects units and simply cap the maximum volume of a track to prevent clipping.

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