Speech Filter

Description 

The human speech apprehend a small area of frequencies, that is extended from 300HZ until 3KHZ. This spectrum is also internationally recognized for the transmission of speech via telecommunications networks. This is also the mainer use of this circuit, one and it can be used in uses that we needed this concrete spectrum of frequencies, rejecting the spectrum on and under what, making comprehensible the speech. The circuit is constituted by two active units, filters of second class (calculated for critical damping). The first filter round the IC1A rejects the low frequencies (under 300 HZ) [high pass] and the second IC1B high (above 3KHZ) [low pass], composing thus a total filter band pass of area (300HZ-3kHZ). In order to has good yield the filter, as with all the filters, it should are used resistances metal film 1% and capacitors polysteryne. 

Circuit diagram

Part List

• R1= 120Kohm
• R2= 100Kohm
• R3= 470Kohm
• R4-7= 8.2Kohm
• R5= 6.8Kohm
• R6= 33Kohm
• R7= 150Kohm
• R8= 47Kohm
• C1-2-8= 2.2nF 100V polystyrene
• C3= 150pF
• C4-9= 100nF 100V
• C5-10= 47uF 25V
• C6= 100nF 100V polystyrene
• C7= 560pF
• C11= 150pF
• C12= 10uF 25V
• IC1= TL072 

 Source http://users.otenet.gr/~athsam/speetch_filter.htm