Bug 2138 – Crossfade Tracks effect may desynchronize tracks

••• Introduction •••
••• Keywords •••

Audacity 3.0.3 development began 19th April 2021

Audacity Bugzilla

Bug 2138 - Crossfade Tracks effect may desynchronize tracks


Summary:	Crossfade Tracks effect may desynchronize tracks

Status:	RESOLVED FIXED

Product:	Audacity
Classification:	Unclassified
Component:	Built-in FX
Version:	2.3.3
Hardware:	Per OS All

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

URL:
Keywords:	nyquist

Depends on:
Blocks:
	Show dependency tree / graph

Reported:	2019-06-24 16:04 UTC by Steve Daulton
Modified:	2019-06-25 08:22 UTC (History)
CC List:	2 users (show)

See Also:
Steps To Reproduce:	1) Launch Audacity 2) Generate a tone 3) Duplicate the track 4) Make a selection in both tracks, somewhere around the middle of the tone. 5) Apply "Crossfade Tracks" with: * Fade Type: Constant Gain * Fade Direction: Alternating Out/In Depending on the exact length of the selection in step 2, the audio after the fades may become desynchronized by up to 9 samples.
Release Note:
First Git SHA:
Group:	---
Workaround:
Closed:	2019-06-25 00:00:00

Flags:	petersampsonaudacity: Test‑OK‑Win+

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Description Steve Daulton 2019-06-24 16:04:26 UTC

Crossfade Tracks may alter the length of the track that has the fade-out.
In cases where there is additional audio in the track beyond the fade, this is likely to cause the audio beyond the fade to move by up to 9 samples,  which is sufficient to cause phasing problems.

This bug was reported by a user on the forum, so it is a "real world" issue and not just a theoretical issue.

Comment 1 Steve Daulton 2019-06-24 16:09:02 UTC

Fixed at https://github.com/audacity/audacity/commit/7787ea1

Comment 2 Peter Sampson 2019-06-25 05:47:12 UTC

Testing on W10 with audacity-2.3.3-alpha-273-baf4648621892ee3936acd242463abd9a81e3129

This now looks to be fixed with no offset following the steps (zooming in to the sample level at the end of the crossfade and the end of the tracks)

I also tested on 2.3.2 to make sure I understood what the issue was - and here I did observe an offset of a few samples - i.e. de-synchronization.

Comment 3 Peter Sampson 2019-06-25 08:22:43 UTC

This fix is to a Nyquist plug-in and thus should operate the same on all 3 platforms - so closing this on the basis of the success of the W10 tests