Collection of tracks, useful for discussing Mixxx features. They have been either used in community discussions, pushing one musical property to the max or are well known for a particular feature.

https://www.youtube.com/watch?v=xFrGuyw1V8s

This 1976 Disco track is a typical manually played 100 bpm track at that time. It is interesting, because we Mixxx 2.3 beat detector can handle it well. The non const beat mode cycles around 100 bpm makes it useless for auto sync and the a const beat grid is heavily off at many places of the track.

https://sanatonrecords.bandcamp.com/track/already-maged-circle-dance-of-cold-constellations

This is a challenging track for the beat detector, because it is 10:46 long, but has many regions of different BPMs detected by the original QM beat detector. A perfect beat grid hat fully 151 BPM

https://www.youtube.com/watch?v=nrCu94kpE1Q

This is a 1995 Club Mix of Sirtaki, taken from the 1965 movie with the same name. It starts with gentle 105 bpm and speeds up to 180 bpm. It has clear sections, some with constant bpm and some with increasing tempo.

https://www.youtube.com/watch?v=vmDDOFXSgAs

This 1959 Cool Jazz tracks, is the icon for a 5/4 tracks.

The Wikipedia contains a detailed description of the section and phrases structure of the track. https://en.wikipedia.org/wiki/Take_Five

Key: E♭ minor Tempo: 174 bpm

https://www.youtube.com/watch?v=A1OqtIqzScI

This 2004 Punk track is one of the loudest recorded tracks. A mp3 version of this track is clipping after decoding due to the additional noise added by the compression algorithm. The calculated replay gain is -12 dB where a typical values are around -6 dB.

https://www.youtube.com/watch?v=sfR_HWMzgyc

This 1975 Classic Rock track, is an icon for a polymetre track where two metrics are played simultaneously. In this case, the drummer plays a 4/4 measure while the rest of the band is at 3/4.

https://www.youtube.com/watch?v=PivWY9wn5ps

This 1987 Electronic Pop track has on of the most famous key change. It comes along with a "CHANGE" in the lyrics at ~2:45. The key changes from G Major to A♭ Major.

https://sanatonrecords.bandcamp.com/track/procs-frigolitpuffens-magiska-trampdyna

This is a challenging track for the beat detector, because it is has 139.98 BPM instead, and must not be rounded to 140,00 BPM for an optimal beat grid. This track is a good example why too aggressive rounding is not always a good solution.

https://subjoi.bandcamp.com/track/empty-nights

Mixxx 2.3 beat detection fails to detect downbeat and places beatgrid on offbeats instead. BPM 126.0 correct. Key falsely detected as Bb while it is Gm (parallel minor). Track changes between chords Gm and Dm. Stacking both chords and using Bb as root that results in Bbmaj713. So maybe stronger emphasis on root tone could help identify correct key in this case.

https://www.youtube.com/watch?v=GxZuq57_bYM

This is the b-side of the chart single "Color Him Father" from 1969. It contains the most used sample (> 2000 times) of all: the "Amen Break". It consists of just 8 beats starting at 1:27.

After these breaks, a odd measure follows that shift the downbeat by a half beat. A normal 4/4 measure is played and that a odd measure shifts the downbeat back to the original position.

https://twoshell.bandcamp.com/track/missing-in-action

With Mixxx 2.3 this track is detected false with 130.08 BPM. This is because the track has non rhythmic bridges an a rhythm that make it hard to decide for a onset as beats. The phase of the the detected beats by QM is shifted throughout the regions of the track.

The rounding code has no access to the onsets and tries to find a common BPM that aligns with most of the beats from QM leading to a 130.08. It cannot round to 130, because than the the annotate beats are off with the QM detected beats.

Key changes:

https://www.classicfm.com/discover-music/music-theory/best-key-changes-pop-song

Skipped or added beats:

https://www.youtube.com/watch?v=ec7wiBkHLC4