> With the inexpensive sound cards, the different inputs are not
> connected to separate A/D converters. You cannot use the Microphone
> input at the same time as the Line-in, for example. There is only a
> single A/D in the chip, and that common A/D converter is switched
> between the different input pins of the chip (often with different
> preamplification gains).
In the Windows (Vista and Windows 7) world, the operating system
enforces "one active input per device" even if the device has
multiple A/D converters and mixer unless the software developer
writes custom drivers and uses the "exclusive hardware access" mode.
All of the "normal" amateur software uses standard operating system
access and enables/disables (switches) inputs to the single A/D
converter anyway. The lack of multiple A/D is not an issue for
the software amateurs "expect."
73,
... Joe, W4TV
On 8/4/2010 9:19 PM, Kok Chen wrote:
>
> On Aug 4, 2010, at 12:49 PM, Joe Subich, W4TV wrote:
>
>> Separate microphone input and analog Line Input which can be
>> selected by the operating system. Those cards with separate mic
>> and line inputs are "three port" cards - Mic In, Line In and Line
>> Out (or speaker/headphone output).
>
> With the inexpensive sound cards, the different inputs are not
> connected to separate A/D converters. You cannot use the Microphone
> input at the same time as the Line-in, for example. There is only a
> single A/D in the chip, and that common A/D converter is switched
> between the different input pins of the chip (often with different
> preamplification gains).
>
> An additional thing to look out for is that while these chipsets
> provide a stereo input when Line-in is selected, the microphone input
> is often mono only.
>
> For example, on Mac OS X, a Micronas
> (http://www.semiconductorstore.com/pdf/newsite/Micronashal/uac355xb_2pi.pdf)
> based sound card appears as a stereo sound card when Line-in is
> selected, but drops to become a mono sound card when the microphone
> input is selected. These switched inputs are called "Sources" on Mac
> OS X to distinguish them from real multi-channel or multi-stream
> inputs.
>
> 73 Chen, W7AY
>
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>
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