[ardour-users] 48 channels on ardour

John Rigg au at sound-man.co.uk
Tue Jul 17 16:04:47 PDT 2007

On Tue, Jul 17, 2007 at 02:17:44PM -0700, Kevin Cosgrove wrote:
> On 17 July 2007 at 20:04, John Rigg <au at sound-man.co.uk> wrote:
> > Yep. You'd have to decide if you really need to use 96kHz rather
> > than 48kHz. With something like a Delta 1010, most of the potential
> > increase in quality at 96kHz is wiped out by the increased clock
> > jitter, so it isn't really worth using more than 48kHz with that
> > particular hardware.
> Very interesting.  Is there much additional jitter from trying to 
> sync multiple units, or is the internal jitter of one unit enough to 
> degrade the quality?  How are you determining the quality differences 
> between 48kHz and 96kHz?  Are you looking at the noise floor?  Or, 
> maybe you've run a test like "effective bits"?  See http://www2.tek.com/cmswpt/tidetails.lotr?ct=TI&cs=Application+Note&ci=4405&lc=EN&from=rss

I haven't done extensive comparisons between 48kHz and 96kHz,
but I didn't hear enough of a difference between them to justify
doubling the disk bandwidth and space.

The Delta 1010 does have a jittery clock implementation. That's what
happens when the clock is on the PCI card and the converters are at
the other end of a 3m cable, with HF losses and crosstalk with all
the other signals in the cable contributing to jitter. I got a
noticeable improvement in audio quality just by replacing the 3m
host cables with 1m ones.

Regarding jitter when syncing, the 1010s sound better when using internal
clock than when synced via either BNC or S/PDIF. If I don't need more
than eight channels (eg. when overdubbing) I run jackd with only one
Delta 1010, set to internal clock. This situation can't be completely
remedied by using a high quality external clock, because jitter occurs
in the cable and the Delta 1010 hasn't got very good jitter attenuation
on its S/PDIF or wordclock inputs. It can be minimised by syncing with
very short, well-shielded cables with low capacitance.

> > Yes. At least one user on these lists is using it for 64 channels.
> > I'm currently using three Delta 1010s for 24 tracks. It's reliable
> > and I don't get xruns (I use large period size and monitor from the
> > 1010s' hardware outputs for `zero latency' monitoring though). Having
> > said that,
> Are you sync'ing your three via the BNC sync connectors or through 
> the S/PDIFs?

When using all three 1010s I clock them from an Audiophile 2496 card
(also ice1712) in the same box, via a home-made 3-way S/PDIF splitter.
That way all three 1010s receive their clock signals at the same time.
As a bonus the 2496 also bumps the 1010s off the IRQ that is shared by the
graphics and network adaptors onto individual IRQs of their own. I'm not
using the 2496 for I/O in this configuration.

This is getting a little OT, but feel free to email me off list if you
have more 1010-specific questions.


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