The audio examples in this presentation were prepared using the GoldWave digital audio editor version 4.26. (www.goldwave.com) Click this icon to verify that your sound works.
Square wave before filtering
Square wave after low-pass filter
The GoldWave Device Controls panel Spectrum (1 kHz square wave) Spectrum (1 kHz sine wave)
HPF (2.7 kHz) LPF (500 Hz) 400 Hz Square wave Filtered wave (sine) Audio example (square wave and filters) Click the speaker icons to hear the sounds. The low-pass filter attenuates all harmonics higher than the 1 st (the fundamental). Filtered wave The high-pass filter passes the 7 th harmonic and all those above. BPF (2.0 kHz) Filtered wave (sine) The band-pass filter passes the 5 th harmonic
LPF (2 kHz) Voice Filtered Voice Audio example (voice and low-pass filter)
HPF (500 Hz) Voice Filtered Voice Audio example (voice and high-pass filter)
BPF 0.5 - 2 kHz Voice Filtered Voice Audio example (voice and band-pass filter)
Voice Voice with echo Audio example (echo effect) An echo effect is created by adding delayed samples to the original signal. Delay
Reverse Voice Reversed Voice Audio example (voice and reverse effect) The reverse effect flips the end of the sampled signal with the beginning (thus it plays backwards).
Voice Noise Voice + Noise Audio example (voice + noise) LPF (2 kHz) The noise is broad band and a LPF only helps a little.
The importance of signal-to-noise ratio Very poor Very good
Voice Clicks Voice + Clicks Audio example (voice + clicks) Click DSP The removal of clicks with DSP works very well.
BSF (1 kHz) Voice 1 kHz sine Voice + 1 kHz sine Audio example (voice + 1 kHz sine) The removal of an interfering tone with a band-stop filter works very well but there is some ringing.
Pitch higher Voice Altered Voice Audio example (voice and special effects) Pitch lower Altered Voice The pitch is changed by clocking the data to the D/A converter at a faster or slower rate.
SE #1 400 Hz square wave Audio example (400 Hz square wave and special effects) SE #2 SE #3 SE #4 If you can imagine it, DSP can probably do it!