Rockbox mail archive
Subject: Re: S/PDIF sync'ing
From: Neon John (johngd_at_bellsouth.net)
On Wed, 14 Jan 2004 22:10:46 +0100, Joris van den Heuvel
>I have a question about connecting the digital out of a JBR20 to an S/PDIF device. Recently I decided to give this a try in my mini home studio. The (fully digital) mixing board has 2 S/PDIF inputs. Everything works fine (exactly 0dBFS on the mixer, nice!), until a track change. At this point, playback stops, the mixer has to resync, which lasts about 5 seconds. In those 5 seconds, there's no sound, as the mixer suppresses the unsynced (probably garbled) audio. The same thing happens upon pausing playback.
>My guess is that the JBR interrupts the S/PDIF clock and the mixer loses synchronisation. Is there a way to have the S/PDIF clock run constantly? Or is this a MAS3587 "feature"? It makes the digital port useless.
>Maybe it's the mixing board that's at fault, I don't know.
I have considerable experience with TOS/Link between a sound card and various
Sony MD players. TOS/Link, as I understand it, is S/PDIF over a fiber optic
Sync was essentially instantaneous. My sound card turned off the light
whenever there was no audio. The MD recorder could be set to start recording
on the presence of TOS/Link input. It never missed even the first note. I
did some playing around one day to see how far the light beam would reach from
the end of the fiber. I could get it an inch away from the MD input jack
before it dropped out. As I moved the fiber into and out of range, the sound
came and went instantly, just like a squelch action.
I also have some S/PDIF input surround sound speakers. My Jukebox drives them
just fine. They do not require any sync time. I can plug the S/PDIF jack in
the jukebox while it's playing and the sound is there instantly.
Sounds to me like there is some problem with the mixer. It shouldn't take
more than one or two frames for the clock to sync and that happens so fast as
to be essentially instantaneous. I wonder if the signal level is on the edge.
It could be that the Jukebox output level varies a bit as the drive spins up,
etc. That might take the signal into and out of the slicer in the mixer. It
may take a few seconds after the hard drive spins down for the battery voltage
to recover enough.
John De Armond
Cleveland, Occupied TN
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