[LAU] JACK: inputs and outputs

[Patrick Shirkey]

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