Re: [LAU] JACK: inputs and outputs

On 07/18/2010 09:46 PM, Andrew Bryant wrote:
> If I use qjackctl to start jackd, the connect window shows two capture
> ports and two playback ports.
>
> I can then start a pair of meterbridge dpms, and connect their inputs
> to the capture ports. Signal applied to the mic jack then shows up on
> the meters. So I deduce that the capture ports are related in some
> way to the mic jack.
>

They are capturing whatever is being sent to the internal digital input
of the device. So anything you have enabled in the mixer settings [line
in, mic, cd] will be heard in jack.

> If I connect between the capture ports and the playback ports, should
> I then expect the signal to be present at either the headphone or the
> line output jack?
>

Yes, if you have unmuted the master output and turned up the pcm
channel. Some cards also have additional input controls that need to be
tweaked.

> And (this may actually be the same question), the soundcard has
> numerous analogue inputs (mic, line, CD), at least two outputs, not to
> mention whatever the mechanism in the digital domain is to relay
> internet radio etc. Can they all appear as ports in the qjackctl
> connect window? Is there some special imprecation needed when I start
> jackd?
>

This is dependant on the card. If it is a multichannel device then you
may see multiple inputs but for most(all) consumer cards the inputs are
mixed at hardware level and presented as one (stereo) to jack.

-- 
Patrick Shirkey
Boost Hardware Ltd
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