# Audio filter from 1Khz to 7 Khz

#### august

Joined Aug 8, 2009
2
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

#### fanie

Joined Jan 20, 2007
63
i am newbie here
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

#### bertus

Joined Apr 5, 2008
19,939
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

#### Jony130

Joined Feb 17, 2009
4,925
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​

#### bertus

Joined Apr 5, 2008
19,939
Hello,

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

Greetings,
Bertus

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#### hgmjr

Joined Jan 28, 2005
9,029
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
It would be useful for you to provide us with some information on your application for this band-pass filter.

hgmjr

#### august

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

#### hgmjr

Joined Jan 28, 2005
9,029
I favor the approach recommended by bertus.

hgmjr

#### jpanhalt

Joined Jan 18, 2008
7,691
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