vahidkh6222

Hello every one
I have two questions please:
1) I need to record two channels simultaneously. I have two mono MICs and since I see balancing bar under MIC/Line In section of "volume control" I assume that my sound card(an onboard realtek HD) is stereo. My laptop has 2 plugin ports, one for MIC and one for Headphone.
I use a 2/1 (mono to stereo) converter to plug these two MICs to single MIC input port. What I get using sound recorder is the "addition" of these two MICs on both recorded channels… but I think and I need to get each mic on separate channels. What do you think the problem is? (the same happens when I plug one MIC two MIC input and another to headphone plugin port)

2) My other question is, do sound cards have flexible sampling rates? I mean, using MATLAB, I can configure the sampling rate and bits per sample of recorded sound. Is it true? I mean, can we really control the sampling rate? I thought it must be fixed….

3) where can i learn more about such matters?

thanks in advance

Maddogg6

First off - is the headphone plug also a mic input jack - I have doubts, it would be a first for an onboard sound to have 2 mic inputs. At best its also a 'line in' - so why hook up a mic to a line in?

The other thing is - if the mic has a plug with 3 connections - its not the same connections as headphones or line inputs. One of the connections on the mic is for a power supply.
If the mic has 2 connections - it probably still wont work becuase mics are a much weaker signal than line level signals and mics need extra amplification that line inputs dont provide for.

The 3 connections on headphones and line inputs are
Gnd, Left & right. vs
Mic Gnd V+

The splitter splits the left and right and uses a common ground, where both mics need the 3rd connection - but is split - so wont work.

Your only (simple) solution is some sort of mixer made for your mics and can PAN them left to right, and output a line out that could connect to your PCs line in - presuming you have a line in - to do what I think you are looking to do.

Google 'audio signals' - and 'audio mixing' should get you some info that would be helpful.

jiiteepee

Mic ports are normally mono. IIRC, on some integrated audio codecs there is stereo microphone input possible as well but, I can't remember if there are just two mic input ports or is it a custom connection.

If you want to use two mono microphones there, you need to get a mic-preamp w/ two mic input ports / stereo line level output port. Connection would then be through line in port into realtek. If there isn't stereo line in port available then you need to get an external audio interface (USB or Firewire) or a PCMCIA/Express card solution.

I suppose this depends on driver and hardware capabilities.
On windows audio, streams that go through kmixer (I don't know Vista audio system) becomes re-sampled to a fixed sample-rate. This happens when you're using MME or DirectSound drivers (on some cases, version 2 from DirectSound drivers is able to bypass kmixer). I don't remember which driver models MatLab supports but, if it uses one of these then sample-rate comes fixed by the kmixer.

Some common driver modes, as like ASIO and WDM/KS (Kernel Streaming mode), bypasses kmixer functionality so, if the hardware supports free sample-rates and has this type driver compatibility then it should be possible to set the sample-rate freely.

IIRC, there are cards, as like Lynx ONE/TWO, that allows user have full control over sample-rate settings ...


jiitee

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vahidkh6222

thanks for your help. then i guess i should...
but i still dont understand, why is there "Left/right" bar in Mic/LineIn section of "volume control", if it is mono? obviously the physical connection is stereo but two channels are experimentally "ADD UP" with each other? (i took one microphone to another room and tested all the combination with spliter and i always had the sound of both two rooms)

dj_stick

the mic input is mono, but when it's mixed back in the onboard sound chip it's output as stereo, with left and right being equal

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jiiteepee

Hmm... because the LineIn port is type of stereo. Having Mic and LineIn port in one jack connector means just that it's a "FlexiJack" type connector in question.


jiitee

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