R24 (perhaps all ZOOM machines), are BPMs what they are supposed to be??

All flavors of Zoom MRS gear discussed here, including MRS-8, 1044, 1266, 1608, etc.
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MaintConsul
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R24 (perhaps all ZOOM machines), are BPMs what they are supposed to be??

Post by MaintConsul » Mon Jan 26, 2015 5:09 pm

Another advantage of the MRS1266 over the R24 was that you could record a master track, then time-stretch it to a faster or slower speed. With the R24 you have to time stretch all tracks, before recording the master track. And there is a story to that as well….
When you record a song in the MRS1266, at a certain BPM (Beats Per Minute), all tracks are at that rhythm. After I converted one song with CodeKiddie's program from DAT to WAV, and assigned the tracks to R24 tracks, I finally decided to try the time stretching on the R24 from 120 to 135 BPM. One positive of the R24 is that it allows to time stretch ALL tracks at once, which is what I selected. To my (naïve?) surprise, I got a message that two tracks would be outside of the limits, would I still like to continue? I did and found that all instrumental tracks had sped up to one speed and all vocal tracks were at another, so the two components were out of synchronisation. I tried it twice more, once doing one track at a time, with the same result. Finally I remembered vaguely that the R24 manual states that it calculates the BPM of a song and that, if the real BPM is different, you need to manually reset it to the correct BPM. I had assumed that this affected the complete song, but on p60 it mentioned “The BPM of each track is automatically calculated when an audio file is assigned to it.” So I went into each track and found that, although all tracks were recorded at 120BPM, the R24 came up with: 128 (2 tracks), 157.8 (2 tracks), 132.1 (2 tracks), 133.8 and 156 BPM. You have to reset them all by using the Track button, then go down to BPM. Empty tracks are always at 120 BPM. In other songs I found a range from 93 to 170BPM.
Then I found that using the time stretch default value of ‘beat’, results in a sound that has some ‘under-water’ effect in it. A proper time stretch, without any kind of distortion results from changing this to ‘tone’, but the default is ‘beat’.
I thought this was all there was to know, but stranger things happened yesterday. I had a song that I had recorded years ago at 110BPM. Perhaps this was wrong, as I could not get this to match with a drum rhythm on my keyboard. It was in-between 94 and 95. Looking at the BPMs in each track, they varied mostly between 97.7 to 98.1, so I decided to manually set them all to 98 BPM. After this, I time-stretched them all at once to 95BPM, using ‘Tone”. The result was good, until I tried to record a new drum track from my keyboard at 95 BPM, and both rhythms were way out. This time I tried for over 45 minutes to match it to an R24 drum pattern and finally found that ‘95BPM’, that it time stretched to, matched 70.4 actual BPMs. I then set all tracks to 70.4 and time-stretched to 74BPM, and then the R24 finally matched the 74BPM from the keyboard. I do not understand why in the first stretch from 98 to 94BPM, the actual BPMs were over 24BPMs lower than 95, but in the second stretch they matched perfectly. It seems ZOOM uses a multiplier, such as 95/98 = 0.9693877551020408 and apply that to whatever the original BPM was (but that would not have resulted in 70.4!!). So, it seems that you can't trust ZOOM's BPMs as a result of a time stretch and you always need to check the outcome against another, known, BPM source, such as a keyboard.
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