Voice Bandwidth Filter


Posted on Feb 5, 2014

This circuit passes frequencies in the 300Hz - 3. 1kHz range, as present in human speech. The circuit consists of cascaded high-pass and low-pass filters, which together form a complete band-pass filter. One half of a TL072 dual op amp (IC1a) together with two capacitors and two resistors make up a second-order Sallen-Key high-pass filter. With the


Voice Bandwidth Filter
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values shown, the cut-off frequency (3dB point) is around 300Hz. As the op amp is powered from a single supply rail, two 10kO resistors and a 10 µF decoupling capacitor are used to bias the input (pin 5) to one-half supply rail voltage. The output of IC1a is fed into the second half of the op amp (IC1b), also configured as a Sallen-Key filter. However, this time a low-pass function is performed, with a cut-off frequency of about 3. 1kHz. The filter component values were chosen for Butterworth response characteristics, providing maximum pass-band flatness. Overall voltage gain in the pass-band is unity (0dB), with maximum input signal level before clipping being approximately 3. 5V RMS. The 560O resistor at IC1b`s output provides short-circuit protection.




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