How to record very faint sound from the analogue input?

[Dotan Cohen]

On 7 March 2010 17:20, Joep L. Blom <jlblom at neuroweave.nl> wrote:
> Hakan Koseoglu wrote:
>> Dotan,
>> On Fri, Mar 5, 2010 at 6:59 PM, Dotan Cohen <dotancohen at gmail.com> wrote:
>>> I need to record a phone conversation, but the sound from the analogue
>>> input is so weak that recording and playing back in Audacity I hear
>>> almost nothing. How can I either boost the playback or (even better)
>>> boost the input so that the file is recorded in a hearable way?
>>
>> Your best chance is to boost the signal before it arrives to the
>> microphone input. You should be able to get one from your local Radio
>> Shack-clone or if you want to do it yourself
>> (http://www.epanorama.net/circuits/micamp.html)...  Also make sure
>> that the impedances are not way off. That would increase the loss even
>> further.
>>
>> Software solutions will invariably end up with a LOT of noise since
>> you will be amplifying all of the internal noise from your PC/laptop.
>> I always found that making sure that the incoming voltage level is
>> good before recording at my home studio. Since your signal to noise
>> ration is so horrible, whatever modification you do after it gets
>> converted to digital (i.e., pulse audio mixer settings or Audacity
>> levelling), you will just amplify the noise along with the signal. Do
>> it before it arrives to the PC.
>>
> I agree with Hakan. A bad signal is never improved by digital
> amplification: it only amplifies the noise.
> However, it could be a good idea only to match the inpput impedance of
> the signal output to the audio input. I would never use the microphone
> input for a line signal as:
> 1.      The impedance matching is normally way out
> 2.      The analog signalpath is especially adapted to the microphone signal
> which is much differeing from a line signal.
> with 3 resistors and a transistor a simple impedance matching circuit
> can be build. You don't need a cicuitboard. A soldering iron and some
> wires is sufficient.
> Joep
>
>

I can solder! If you can recommend or link to a wiring diagram, I can build it!

Thanks!

-- 
Dotan Cohen

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