[Ardour-Users] punch-in with hardware monitoring - latency problem

plutek-infinity plutek at infinity.net
Mon Dec 1 07:12:30 PST 2008

>Date: Mon, 1 Dec 2008 11:46:29 +0000
>From: John Rigg <au at sound-man.co.uk>

>On Fri, Nov 28, 2008 at 12:19:37PM -0500, plutek-infinity wrote:
>> replying to myself.... i see in http://osdir.com/ml/audio.ardour.user/2005-04/msg00143.html paul's comment:
>> "you cannot do zero latency input monitoring *and* playback on
>> the same channel. the hardware just doesn't allow it."
>This refers to the fact that the sound card's internal routing
>only allows a given hardware output to be connected to one
>signal source at a time. You can connect it to either the internal
>mixer output or an alsa pcm output, not both at once.
>Here it means that Ardour's master outputs can't be connected
>to the same hardware outputs as the RME card's internal mixer,
>but have to be routed to the appropriate mixer inputs instead.

hmmm... well, with the Multiface, the outputs to which we connect in Jack are not physical outputs, but rather are software "playback" outputs, which we then connect as we wish to physical outputs within the unit's internal mixer. so, we can mix those "playback" channel sources with our input channel sources for near-zero latency monitoring of input signals while hearing playback of previously recorded material from the same physical outputs. ardour then auto-compensates for the latency between those two sources when placing the new material in a playlist. at least that's how i understand it -- sorry if i'm telling you stuff you already know, or if i'm quite incorrect!

i was guessing that what ends up happening in a punch-in situation is that the track being recorded to is started in a sync position which is aligned with the other recorded tracks, and when it is asked to record (by toggling the transport record function), it cannot then suddenly switch its sync position to an earlier, latency-compensating position. otoh, when the transport is *started* in record mode, perhaps it's is in a latency-compensating time relationship to the other tracks when it starts rolling, so the new material gets put in the correct spot. however, i now know that's not the explanation, because if i *start* transport in record mode and then toggle transport-record off while still rolling, the playback of the rest of the track IS in sync, so that explanation doesn't make sense.

would anyone ( paul?? ;)  ) care to explain how this all works?

sorry to keep hammering away at this, but i'd really like to understand what's going on !



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