# Audio filter from 1Khz to 7 Khz

Discussion in 'The Projects Forum' started by august, Aug 9, 2009.

1. ### august Thread Starter New Member

Aug 8, 2009
2
0
Please help i am newbie here. I need design audio filter which only work in 1 Khz till 7 Khz. Can anyone here help me pls!

thx!

august

2. ### fanie Active Member

Jan 20, 2007
63
0
Nice excuse

Do a search for Filter Lab. You can design a high and low pass filter from that.

There are about 3 different filter programmes (freeware) you can use. Some just works easier

3. ### bertus Administrator

Apr 5, 2008
17,722
3,282
Hello,

I think you will have to split it up.
Use a highpass filter of 1 kHz with a lowpass filter of 7 kHz behind it.

Here is a page from the EDUCYPEDIA with information on filters.
http://www.educypedia.be/electronics/analogfil.htm

Greetings,
Bertus

Jan 18, 2008
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May 11, 2009
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6. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,296
1,228
Maybe this circuit will be enough

$R1=\frac{Q }{2*\Pi*F*C1*Ku}$

$R2=\frac{Q }{2*\Pi*F*C1(2*Q^2-Ku)}$

$R3=\frac{Q }{\Pi*F*C1}$

Or simplified equations

$R1=Xc*\frac{Q }{Ku}$

$R2=Xc*\frac{Q }{2*Q^2-Ku}$

$R3=Xc*2Q$

Where:
C1=C2
$Xc=\frac{1 }{2*\pi*F*C}$

Ku=gain

B=Bandwidth=Fg-Fd=7KHz-1KHz=6KHz

Fo=4Khz

$Q=\frac{f0}{B}$

$f0=\frac{1}{2*\Pi*C}*\sqr{\frac{1}{R3}*(\frac{1}{R1}+\frac{1}{R2})}$

Or this simple circuit

FL= lower cut-off frequencies = 0.16/(C1*R1)

FH= upper cut-off frequencies = 0.16/(C2*R2)

Au=gain=R2/R1​

7. ### bertus Administrator

Apr 5, 2008
17,722
3,282
Hello,

You can also read the attached PDF from TI on filter design.

Greetings,
Bertus

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8. ### hgmjr Moderator

Jan 28, 2005
9,030
217
It would be useful for you to provide us with some information on your application for this band-pass filter.

hgmjr

9. ### august Thread Starter New Member

Aug 8, 2009
2
0
Thx A lot!
I want use this filter for My Swiftlets sound system.

10. ### hgmjr Moderator

Jan 28, 2005
9,030
217
I favor the approach recommended by bertus.

hgmjr

11. ### jpanhalt Expert

Jan 18, 2008
5,776
940
FilterPro by TI and sloa096 (filter design application note by TI) are joined at the hip, so to speak.

Going through the calculations can be fun. The sequential process for a design described in the note is particularly helpful. FilterPro gives a graphical presentation of the response and calculates the gain bandwidth product (GBP) needed for the op-amp. I found the comparison of filter types and ability to readily observe how the response changes with different variable inputs particularly educational.

I suggest the OP go through the calculations for a simple design, but then use a program such as FilterPro to finalize his design. Note especially the effect of component tolerances on your actual results. You may need to tweak some values.

John