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Old 22nd March 2008, 09:17 PM   #1
newsci is offline newsci  United States
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Default 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 ?
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Old 22nd March 2008, 10:22 PM   #2
AndrewT is online now AndrewT  Scotland
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I'm guessing this is not for music?
What is it for?
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Old 25th March 2008, 07:29 AM   #3
newsci is offline newsci  United States
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No its for speech...its basically after desccrambling of voice message over wireless
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Old 25th March 2008, 10:56 AM   #4
AndrewT is online now AndrewT  Scotland
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frequency response 300Hz to 3kHz as in telephony or a bit wider?
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Old 25th March 2008, 08:47 PM   #5
newsci is offline newsci  United States
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yah upto 4 Kz not more...its over wireless
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Old 26th March 2008, 08:28 AM   #6
AndrewT is online now AndrewT  Scotland
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low pass at 40kHz (RC=4uS).
What about your high pass?
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Old 26th March 2008, 08:40 AM   #7
newsci is offline newsci  United States
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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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Old 26th March 2008, 09:18 AM   #8
AndrewT is online now AndrewT  Scotland
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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.
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Old 1st March 2014, 10:09 AM   #9
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Default lm386 amplification and filter circuit

I am using lm386 for signal amplification recievied from microphone and then send them to analog pin of arduino..do i need a speech filter circuit also between lm386 and arduino or lm386 would limit the frequency response to 300-3400hz (the speech audio spectrum range)??....
{ basically i am trying to make a audio recorder..the arduino will store the data in a wav file and transfer it to sd-card for playback }..
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Old 1st March 2014, 11:24 AM   #10
AndrewT is online now AndrewT  Scotland
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The input to any receiver along the route could be susceptible to interference.
I suggest you fit RF attenuation at every input.
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