View source for Lowpass filter

Lowpass filter is used to cut off the higher frequencies, and "pass" the lower frequencies. In Lossy audio it is used to lower the [[bitrate]] demand or to spare bits for the lower more important frequencies. Young people can hear a loud sine wave up to 21-22kHz. The same people can't normally distinguish any difference between 19kHz lowpassed music and non-lowpassed music.

[[Image:Fft_lowpass.png|frame|none|Figure 1: FFT analysis (Frequency-Amplitude domain)]]

The figure on the left side does not have a any lowpass used, while the figure on the right is signal filtered with 15kHz lowpass filter.

[[Image:Spectral_lowpass.png|none|frame|Figure 2: Spectral view (time-frequency domain)]]

The figure on the left side does not have a any lowpass used, while the figure on the right is signal filtered with 15kHz lowpass filter.


A good tool for applying lowpass on audio streams is [http://sox.sourceforge.net/ SoX]