filtering before LM386?

newsci · 22nd March 2008, 10:17 PM

Hey,
im working with LM386.The output comes from 8bit DAC and i need a low pass series RC filter i suppose.The sampling rate is 8000/sec
Can anyone tell me the values for the filter ?

AndrewT · 22nd March 2008, 11:22 PM

I'm guessing this is not for music?
What is it for?

newsci · 25th March 2008, 08:29 AM

No its for speech...its basically after desccrambling of voice message over wireless

AndrewT · 25th March 2008, 11:56 AM

frequency response 300Hz to 3kHz as in telephony or a bit wider?

newsci · 25th March 2008, 09:47 PM

yah upto 4 Kz not more...its over wireless

AndrewT · 26th March 2008, 09:28 AM

low pass at 40kHz (RC=4uS).
What about your high pass?

newsci · 26th March 2008, 09:40 AM

do i need one..i just needed the reconstruction filter.ITs a speech scrambler and descrambler.Well what exactly is the R and C value?

AndrewT · 26th March 2008, 10:18 AM

for RC=4.4uS, try R=2k0 and C=2n2F
If R=2k0 does not suit, then scale the numbers.
The RC does not need to be exact. It does not matter whether it is 9times or 11times the max speech frequency.

22nd March 2008, 10:17 PM	#1
newsci diyAudio Member Join Date: Mar 2008	filtering before LM386? Hey, im working with LM386.The output comes from 8bit DAC and i need a low pass series RC filter i suppose.The sampling rate is 8000/sec Can anyone tell me the values for the filter ?

22nd March 2008, 11:22 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	I'm guessing this is not for music? What is it for? __________________ regards Andrew T.

25th March 2008, 11:56 AM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	frequency response 300Hz to 3kHz as in telephony or a bit wider? __________________ regards Andrew T.

26th March 2008, 09:28 AM	#6
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	low pass at 40kHz (RC=4uS). What about your high pass? __________________ regards Andrew T.

26th March 2008, 10:18 AM	#8
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	for RC=4.4uS, try R=2k0 and C=2n2F If R=2k0 does not suit, then scale the numbers. The RC does not need to be exact. It does not matter whether it is 9times or 11times the max speech frequency. __________________ regards Andrew T.


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25th March 2008, 08:29 AM	#3
newsci diyAudio Member Join Date: Mar 2008	No its for speech...its basically after desccrambling of voice message over wireless

25th March 2008, 09:47 PM	#5
newsci diyAudio Member Join Date: Mar 2008	yah upto 4 Kz not more...its over wireless

26th March 2008, 09:40 AM	#7
newsci diyAudio Member Join Date: Mar 2008	do i need one..i just needed the reconstruction filter.ITs a speech scrambler and descrambler.Well what exactly is the R and C value?

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