Changing tempo when using instant double and sync

[mixxxbot]

Reported by: daschuer
Date: 2021-10-07T17:58:08Z
Status: New
Importance: Undecided
Launchpad Issue: lp1946385

---

When using instant double and sync is enabled on the source and target deck, the tempo changes every time you repeat the instant double action.
The issue has been recorded here #3944 (comment)

[mixxxbot]

Commented by: ywwg
Date: 2021-10-08T02:02:44Z

---

The issue is that the sync occurs when the track is still seeked at position 0. A possible fix would be to create a way to load a track immediately seeked at the requested position. I don't think that should be too hard.

[ronso0]

Is this still reproducible?

[daschuer]

I can still reproduce the issue with 2.4-beta-96-g75833c0dba

There is also a flanger effect due to a micro offset when quantize is enabled and you instant-double a non const BPM track.
This does not happen every time, it is not reproducible without quantization enabled in the target deck.

Both issue cannot be reproduced with Mixxx 2.3.6

[m0dB]

I ran into this issue some days ago but I have not been able to reproduce it since. The video in #3944 (comment) doesn't load for me. Is there a textual description of the exact steps to reproduce this?

[daschuer]

• Load a track with dynamic tempo to deck A
• Sync Deck A + B
• Make sure Deck A is leader
• Dag and drop Track from Deck A to B

Expected results:
Deck A and B play perfectly synced, increasing the Volume by x2 (6 dB)
(This is the case without Sync)

Actual result:
Deck A applies tempo changes to Deck B resulting in a Flanger sound.

[ronso0]

For me the results is

• both decks get synced to 120 BPM (internal clock default?) in the moment of dropping the track
• deckA is slightly ahead (hence the flanger effect)
• one click on temp_rate_down seems to fix it, at least waveforms seem to be in sync again and the flanger effect is not audible as such, but the stereo depth is gone, mix sounds flat so there IS still some offset

[daschuer]

#12435 aims to fix these issues. Can you confirm this?