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Re: Live recording




On 07/28/17 12:11, Rodolfo Medina wrote:
According to:

 http://www.upubuntu.com/2013/05/how-to-record-your-voice-from.html

I record live sound via microphone just doing:

 $ sox -t alsa default output.wav

Now I was wondering about the stereo o non-stereo character of such a home made
recording...  I tried to use two microphones together, plugging them together
into the PC with a small common connection doubber.  Can we say the result is
stereo...?  I would doubt...  and how to have - if possible - a stereo effect
with the above basic recording instruments?

Connecting two monophonic microphones in parallel with a connection splitter run backwards will yield a monophonic signal with reduced gain and time/ frequency signal artifacts such as comb filtering and echo. For most applications, the result will not be acceptable.


Capturing sound with two microphones can be done several ways:

https://en.wikipedia.org/wiki/Stereophonic_sound#Recording_methods


Computer microphone port(s) are typically monophonic and the line input port(s) are typically stereophonic. If you want to record in stereo, you need to provide left and right channel signals to the line input port.


Computer microphone ports and line input ports also expect different voltages and have different impedance. I believe computer line input ports are designed to consumer audio equipment standards -- e.g. -10 dBV into 10 kOhm for 0 VU:

https://en.wikipedia.org/wiki/Line_level#Nominal_levels


(For microphone ports, my guess would be -30 dBV into 1 MOhm.)


This means you need two microphone pre-amplifiers and/or a stereo mixer with two or more microphone inputs:

https://en.wikipedia.org/wiki/Line_level#Line_level_in_traditional_signal_paths


The audio capabilities of Linux have evolved over the years:

https://en.wikipedia.org/wiki/Open_Sound_System

https://en.wikipedia.org/wiki/Advanced_Linux_Sound_Architecture


Sox is a command-line tool that has been around since 1991:

https://en.wikipedia.org/wiki/SoX


Audacity is my favorite interactive audio recording and editing tool:

https://en.wikipedia.org/wiki/Audacity_(audio_editor)


If you would care to explain your application, we might be able to give more advice.


David