Hiss killer - Low pass filter at knee at about 1 KHz

A low pass RC filter with a corner at 723.432 Hz ----------------------------------------------------------- At 1 KHz there is a -5 dB cut in level At 10 KHz there is a -22 dB cut! This is a hiss killer. Its dramatic effect is noted at 10 KHz where there is a -22 dB drop in signal level. This is rudimentary stone-age filter, yet it does the job for radio applications. --------------------------------------------------------- The effect of the load impedance, shown here as a simple resistance. The load resistance is set a a nominal 30KΩ which is OK for audio applications. If we increase the load resistance to 1 MΩ, the filter characteristics change a little but essentially it does the same job of killing the hiss. Now, if we lower the load resistance to 100Ω, we get the same filter shape, but the main attenuation moves along to much higher frequencies.

published 9 years ago