# Help! The more I search about Speech Filter - the more I get confused! pls help

#### rayagustin

Joined Oct 1, 2017
2

#### DickCappels

Joined Aug 21, 2008
10,167
Hint: You just described the bandpass of the filter you need. Try looking it up and see if that helps.

#### bertus

Joined Apr 5, 2008
22,275

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#### Papabravo

Joined Feb 24, 2006
21,222
The way to start is to develop the actual requirements of the filters. Here is how you do that:
1. What is the corner frequency? For example: 300 Hz.
2. What is the allowable ripple in the passband? For example: None - maximally flat
3. What is the maximum attenuation in the passband? For example 0.3 dB
4. What is the bandwidth of the transition band? For example: 900 Hz.
5. What is the minimum attenuation in the stop band? For example: -40 dB
6. What is the allowable ripple in the stopband? For example: 20 dB
From these requirements you can derive the type of filter, and the order. Then you can test your design to see if it meets the requirements.
Van Valkenburg, M.E.,Analog filter Design

https://www.amazon.com/Analog-Filte...=1506865890&sr=8-2&keywords=Van+Valkenburg+ME

#### rayagustin

Joined Oct 1, 2017
2
Thank you for the replies guys. I made the circuit on a breadboard but somehow I couldn't manage to produce a sound from the microphone to speaker..

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#### DickCappels

Joined Aug 21, 2008
10,167
Are those ohms in your schematic or kilo ohms?

Your opamp can't drive much voltage into a 15 ohm fredback resistor. Multiply the resistors by 1,000 and devide the capacitors by 1,000 and things should start wotking.

After you fix the resistors and capacitors, You may find that your opamp may not be capable of driving the speaker hard enough for you to hear unlesd you put your ear right up against it.