Emu XL-7 & MP-7 User's Group

I've been using Live as an effect rack and driving it from the PX-7
using the PX-7 as the master clock.  Today I froze a couple of synth
tracks to free up some CPU and was surprised to hear them glitching
heavily.  Since the problem seemed to go away when external sync was
disabled in Live I fired up Logic and watched the Logic midi clock
bounce all over a three bpm range while syncing to the PX-7.

Is this normal?  I seem to be getting a very unstable clock signal
from the PX-7.  I tried a separate midi cable to rule that out and
also an empty pattern with no midi data at all on the PX-7 to make
sure it wasn't just a case of choking on too much data.  Neither of
these fixes made any difference.

I usually experience a drift too, but I think that's normal.
Since MIDI is serial I think there's no way to avoid it, even
if clock messages are system realtime commands.
Simply you have to wait to finish transmitting a message before can
initiate the next and once a message is in the queue there's
no way to remove it.

In my setup using AMT8 with USB I experience for example
a drift of max. -2/+1 BPM when tempo is 130.
Slower tempos will do better, of course as you are slowing down.
At higher tempos there's not much difference.

Really MIDI clock is OK for live act but I wouldn't use for studio
work. In that case you can make Live the master and drive the
PX7 from there. PX7 will drifet of course here too, but maybe
the glitches will go in Live.

Regards,

    Zsolt




----- Original Message ----- 

From: "milesegan" <milesegan@...>
To: <xl7@yahoogroups.com>
Sent: Monday, September 25, 2006 8:05 AM
Subject: [xl7] jittery midi clock?


> I've been using Live as an effect rack and driving it from the PX-7
> using the PX-7 as the master clock.  Today I froze a couple of synth
> tracks to free up some CPU and was surprised to hear them glitching
> heavily.  Since the problem seemed to go away when external sync was
> disabled in Live I fired up Logic and watched the Logic midi clock
> bounce all over a three bpm range while syncing to the PX-7.
> 
> Is this normal?  I seem to be getting a very unstable clock signal
> from the PX-7.  I tried a separate midi cable to rule that out and
> also an empty pattern with no midi data at all on the PX-7 to make
> sure it wasn't just a case of choking on too much data.  Neither of
> these fixes made any difference.
> 
> 
> 
> 
> 
> 
> Yahoo! Groups Links
> 
> 
> 
> 
> 
> 
> 
> 
> 
>

It is normal.  Some MIDI interfaces do better than others, as well as some software sequencers are better masters than others.  Don't worry about the tempo display too much.  The XL-7 derives two signals from MIDI Clock, one being tempo, and the other being position.

The tempo signal is only an approximation (calculated by measuring the time between clocks and applying complicated filtering and hysteresis on those measurements).  The tempo value is used to drive things like LFOs, synced FX, arpeggiators, and other non-sequencer things.

The more important signal is position, and that is *exactly* accurate.  There is no computation done on this value, it's simply the count of the clock events it's recieved.  Therefore, if the XL-7 has recieved 24 clocks, it knows that it's exactly at beat two of the first measure, no approximation necessary.  This value drives the sequencer.

In simpler terms, don't stress about the display, it's just a close guess that has little bearing on the internal sequencer!

Hmm, actually, I just re-read your message and noticed that I have it all backwards.  You're slaving Live (or Logic) to the XL-7.  Well, I can't say for sure how those programs handle MIDI sync, but I'd assume it's similar.  Zsolt is right though, I'd slave the XL-7 to the computer since MIDI sequencers can handle tempo changes *much* better than audio playback systems.

-Aaron

----- Original Message ----
From: Zsolt Szabó <Zsolt.Szabo@...>
To: xl7@yahoogroups.com
Sent: Monday, September 25, 2006 3:59:44 AM
Subject: Re: [xl7] jittery midi clock?

I usually experience a drift too, but I think that's normal.
Since MIDI is serial I think there's no way to avoid it, even
if clock messages are system realtime commands.
Simply you have to wait to finish transmitting a message before can
initiate the next and once a message is in the queue there's
no way to remove it.

In my setup using AMT8 with USB I experience for example
a drift of max. -2/+1 BPM when tempo is 130.
Slower tempos will do better, of course as you are slowing down.
At higher tempos there's not much difference.

Really MIDI clock is OK for live act but I wouldn't use for studio
work. In that case you can make Live the master and drive the
PX7 from there. PX7 will drifet of course here too, but maybe
the glitches will go in Live.

Regards,

    Zsolt




----- Original Message ----- 
From: "milesegan" <milesegan@...>
To: <xl7@yahoogroups.com>
Sent: Monday, September 25, 2006 8:05 AM
Subject: [xl7] jittery midi clock?


> I've been using Live as an effect rack and driving it from the PX-7
> using the PX-7 as the master clock.  Today I froze a couple of synth
> tracks to free up some CPU and was surprised to hear them glitching
> heavily.  Since the problem seemed to go away when external sync was
> disabled in Live I fired up Logic and watched the Logic midi clock
> bounce all over a three bpm range while syncing to the PX-7.
> 
> Is this normal?  I seem to be getting a very unstable clock signal
> from the PX-7.  I tried a separate midi cable to rule that out and
> also an empty pattern with no midi data at all on the PX-7 to make
> sure it wasn't just a case of choking on too much data.  Neither of
> these fixes made any difference.
> 
> 
> 
> 
> 
> 
> Yahoo! Groups Links
> 
> 
> 
> 
> 
> 
> 
> 
> 
>


 
Yahoo! Groups Links






 











[Non-text portions of this message have been removed]

--- In xl7@yahoogroups.com, Aaron Eppolito <synthesis77@...> wrote:
> Zsolt is right though, I'd slave the XL-7 to the computer since 
> MIDI sequencers can handle tempo changes *much* better than
> audio playback systems.

I think that's the answer.  Seems like Live's warping algorithms just
don't like small variations in clock.  This isn't that big of a deal
in practice because it's not noticable for beats etc and I don't
*need* to warp audio in Live.  I'm just using it as a virtual synth
rack for the PX-7.

Thanks.