Bug 282 – Loop Play loses synchronisation

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Audacity 3.0.3 development began 19th April 2021

Audacity Bugzilla

Bug 282 - Loop Play loses synchronisation


Summary:	Loop Play loses synchronisation

Status:	CLOSED WORKSFORME

Product:	Audacity
Classification:	Unclassified
Component:	Application Core
Version:	unspecified
Hardware:	PC All

Importance:	P4 RepeatableAll
Assigned To:	Default Assignee for New Bugs

URL:
Keywords:

Depends on:
Blocks:
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Reported:	2011-02-12 15:25 UTC by Steve Daulton
Modified:	2018-08-20 11:51 UTC (History)
CC List:	7 users (show)

See Also:
Steps To Reproduce:	create a short tone (say 4 seconds) and silence part of it so that you can identify a specific position when it loops. Select the 4 seconds of audio and start loop play (SHIFT+Space). After it has played through 40 times or so the playback cursor will (probably) be out of synch with the audio playback.
Release Note:
First Git SHA:
Group:	---
Workaround:
Closed:	2018-08-20 00:00:00

Flags:	petersampsonaudacity: Test‑OK‑Win+

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Description Steve Daulton 2011-02-12 15:25:48 UTC

The playback cursor and actual playback position gradually drift out of synch after multiple repeats when using "Loop Play".

Comment 1 Martyn Shaw 2011-05-05 19:53:53 UTC

(In reply to comment #0)
Repeatable here (Win 7).

It might be useful to know how long it takes to drift by, say, 1s for different lengths of clip, and at different sample rates.  My very crude results say:
1 or 2s sample, less than a minute.
4s sample, about 4 mins
8s sample, about 12 mins??
YMMV.  And more accurate results would I think be useful.

I think this is a Port Audio 'looping' problem, from my review of the Audacity code; I don't see that we are doing anything wrong.  Maybe there are other apps that use PA and allow looping?  Do they suffer the same problem?

Comment 2 Peter Sampson 2018-08-09 11:41:43 UTC

I ran the 4 second loop with part silence for 10 minutes on my W10 Laptop
with audacity-2.3.0-alpha-77

and it remained in perfect sync.

Will test later on Mac


@Steve:  can you test on Linux for us please.

Comment 3 Steve Daulton 2018-08-09 11:56:06 UTC

(In reply to Peter Sampson from comment #2)
Working fine for me here, (but I'm using a pretty fast Linux laptop).
I left a 1 second selection looping for several minutes, and as far as I could tell, the graphics and sound remained synchronised.

Comment 4 James Crook 2018-08-09 12:23:05 UTC

Based on Comment 2 and Comment 3, CLOSED - WORKSFORME.

If we see it again, we can open a new bug.