19 Sep
2010
19 Sep
'10
6:17 a.m.
I was reading here:
http://bpmdj.yellowcouch.org/jack.html
and became intrigued. A few questions. I would love to be able to run
with (say) three ordinary USB2 audio-in ports plus my AudioTrak Prodigy
HD2.
1. Can different jackd instances, connect and talk to each other? If I
run four instances of Jackd and qjackctl under four different names, can
I connect them all?
2. In the example at the web page linked above, an "ALSA multi" device
is shown, combining multiple devices into one ALSA virtual device. If
memory and CPU is not an issue, will doing this with one Jackd instance
work better than four interconnected Jackd instances? It seems to me
that this would require a "lowest common denominator" approach to
latency-related settings, and combining PCI and USB strikes me as
possibly troublesome because of the very different needs involved.
J.E.B.
19 Sep
19 Sep
7:23 a.m.
On 09/19/2010 06:17 AM, Jonathan E. Brickman wrote:
I was reading here:
http://bpmdj.yellowcouch.org/jack.html
and became intrigued. A few questions. I would love to be able to run
with (say) three ordinary USB2 audio-in ports plus my AudioTrak Prodigy
HD2.
1. Can different jackd instances, connect and talk to each other? If I
run four instances of Jackd and qjackctl under four different names, can
I connect them all?
No. but you can connect multiple soundcards to one jackd instance using
alsa_in and alsa_out. Note however, that alsa_in/out does resample
(unless the soundcards involved are synchronized by word-clock) and you
loose sound-quality.
(FWIW you can use netjack to connect two or more jackd instances - but
then you still need alsa_in/out because the netjack slaves do not
connect to an underlying audio-device but connect to the master-jack.)
2. In the example at the web page linked above, an
"ALSA multi" device
is shown, combining multiple devices into one ALSA virtual device. If
memory and CPU is not an issue, will doing this with one Jackd instance
work better than four interconnected Jackd instances? It seems to me
that this would require a "lowest common denominator" approach to
latency-related settings, and combining PCI and USB strikes me as
possibly troublesome because of the very different needs involved.
J.E.B.
AFAIK alsa-multi devices only makes sense for soundcards that can be
chained.
It is possible to combine different devices on ALSA level but you'll
most likely get a mess: Different latencies, buffer-sizes etc and
experience drop-outs if the cards are not synchronized.
YMMV. It may not matter to you if you use the 2nd soundcard only for
telephoning or some similar task where you don't care.. but your time is
spend better buying a decent soundcard with enough I/O :)
best,
robin
7:32 a.m.
I thought there probably would be a buffer-size conflict problem with
an alsa-multi situation. But netjack over localhost is an interesting
thought.
J.E.B.
(FWIW you can use netjack to connect two or more jackd
instances - but
then you still need alsa_in/out because the netjack slaves do not
connect to an underlying audio-device but connect to the master-jack.)
20 Sep
20 Sep
10:28 p.m.
On 09/19/2010 07:32 AM, Jonathan E. Brickman wrote:
I thought there probably would be a buffer-size
conflict problem with
an alsa-multi situation. But netjack over localhost is an interesting
thought.
netjack over localhost does not make sense. you can just use jackd on
your primary soundcard and alsa_[in|out] on your secondary. but the
realtime resampling will either chew up insane amounts of cpu, or
degrade the sound, or both. ok for telephony or for listening to
unimportant stuff over small speakers, but not for serious work.
generally, multiple soundcards make sense in three scenarios:
a) you have professional soundcards that can sync to an external source
(sometimes, that could even be spdif), in which case you can use an alsa
multi device without sound degradation.
b) you want to fiddle (possibly including soldering the oscillator
output of one card to the clock in of the next...)
c) you really don't care about the sound quality of the secondary card.
if you want to get real work done, shop for a single multichannel card
instead.
21 Sep
21 Sep
12:36 a.m.
netjack over localhost does not make sense. you can
just use jackd on
your primary soundcard and alsa_[in|out] on your secondary. but the
realtime resampling will either chew up insane amounts of cpu, or
degrade the sound, or both. ok for telephony or for listening to
unimportant stuff over small speakers, but not for serious work.
The point is, with
netjack over localhost there is no realtime
resampling. I have a very high quality PCI sound card with RCA outs,
and when I gig with this rig I don't want to be lugging around the USB
device I'm going to need for additional inputs.
J.E.B.
1:30 a.m.
Hi Jonathan,
On 09/21/2010 12:36 AM, Jonathan E. Brickman wrote:
> netjack over localhost does not make sense. you can just use jackd on
> your primary soundcard and alsa_[in|out] on your secondary. but the
> realtime resampling will either chew up insane amounts of cpu, or
> degrade the sound, or both. ok for telephony or for listening to
> unimportant stuff over small speakers, but not for serious work.
The point is, with netjack over localhost there is no
realtime
resampling.
but you gain nothing. The netjack-slave does not have a soundcard
attached to it. It connects to the master-jack which 'speaks' with the
soundcard. You still need alsa_in/out to connect additional devices.
You can also run two jackd's which connect to hardware directly and use
jacktrip to connect the two jackd's .. and there may even be more
alternatives..
Either way: Unless the sound-cards share the same clock, there is no way
to _not_ resample.
The above statement is true for any audio-interface on any OS.
Sorry to disappoint you.
As Joern outlined, audio clock synchronization can be accomplished by
various means. You can pick up a soldering iron and follow
http://quicktoots.linuxaudio.org/toots/el-cheapo/
or buy dedicated hardware that offers it. The technical term is
http://en.wikipedia.org/wiki/Word_clock
Check the recent thread on LAU 'ambidec:..'
http://linuxaudio.org/mailarchive/lau/2010/9/18/173740
for a cheap solution.
Cheers!
robin
I have a very high quality PCI sound card with RCA
outs,
and when I gig with this rig I don't want to be lugging around the USB
device I'm going to need for additional inputs.
J.E.B.
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5 comments
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participants (3)
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Jonathan E. Brickman -
Jörn Nettingsmeier -
Robin Gareus