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Thread: Why do beatmatched tracks with the same BPM still fall out of phase?

  1. #1
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    Why do beatmatched tracks with the same BPM still fall out of phase?

    Hi everyone!

    First post so apologies for stupidity. I'm trying to learn to beatmatch on Traktor, instead of always using sync! My question is in two parts.
    Firstly, am I right in thinking, beatmatching isn't something you do at the start of the track then leave? It seems however bang on I get two
    tracks, they gradually fall out of phase again, so you have to stay on top of it. I assumed this was because even with the tempo range set to
    only 2%, I can never allign BPMs perfectly, so they will always be running at minutely different speeds. BUT I had two tracks running on exactly
    the same BPM just now, but I still had to keep usign the jog wheel as track B was going was out of phase with track A.

    What's the deal? Is there a way to get more accuracy with the tempo fader? Or should 2% be enough? What am I doing wrong?

    TIA!

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    Moderator pete's Avatar
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    Maths.
    that thing at school that was boring.

    Lets look at 3 cases:

    [1]

    Track 1 is 133 BPM
    Track 2 is 137 BPM

    To match them together I need to reduce the speed of track 2 by 137/133 =1.030075187969925% exactly. ish.

    Being a full-on jedi DJ, I can match these up no problem by measuring the amount of atoms on my pitch fader and adjusting correctly.
    Or just guess and keep them in time by adjusting the pitch fader and platter every now and again so no one notices. the maths.

    And even so...if I get the track to 1.04% that means that it will slip out of time by about 1/10000 of a second for every second that passes. So 10000 seconds to slip out of time by one second. Which is just a bit more than 1 beat at the 133BPM I'm rocking the crowd at. 10000 seconds is 2.78 hours. Aint no dancefloor got time for a track that is 2.78 hours!

    So basically its ok to slip a bit and adjust as you go along.
    Unless you're Carl Cox. Then if you slip a bit then everybody gonna be over you saying that you aint no longer the 3 deck wizard. HOLY JESUS.

    [2]

    Track 1 is at 130 BPM
    Track 2 is at 130 BPM

    Both are pitched up by 4%. Because as every DJ knows, everything sounds better at +4.

    Now on old analog turntables this would be an issue, cos to get both pitch sliders at exactly 4% is a mathmatical impossibility (as we looked at in case 1).
    The only way to get them really close would be to play the tracks at 0% and have the Quartz-lock light on. Because quartz lock makes you a mixing magician where all tracks at the same BPM mix together perfectly. You can call yourself the "quartz-lock warlock" or something,. (but even quartz-lock is subject to maths, so you gonna have to touch the decks a bit...). Math is a b!tch. Or rather you're maths's b!tch.

    On your fancy-pants DVS system, in theory this should not be an issue. Tracks should be locked at the same exact tempo. Both locked at 4%, both locked at 135.2BPM. Because maths. I should be able to go and get a beer and enjoy some sweet pleasure with the groupies and still be holding down a mix like some sorta blending Chuck Norris.

    However, if there is any I've learned in my decades of DJing....nothing about DJ equipment is certain (apart from maths). The only way I have to combat this is to be totally certain of my beatmatching skills. I have to be absolutely sure that even in the caldera of an erupting volcano whilst being pleasured by an army of over-eager valkyries, with belt-drives and broken headphones....I can match 2 tracks in less than 2 seconds.

    Anyways DVS has sync. They didn't invent that by chance. It aint a crime to use it. Unless the DJ Police are around.

    [3]

    You're a famous international DJ/Producer.

    It's all good cos you're playing a premixed CD.

    Even after a while when you've grasped the concept of a mixer, someone has time-stretched all your tracks to 128BPM so you just have to flip the fader over with one hand, and wave like the Queen with the other.

    After all its a 100000$ show, aint no one got time for pitch wheel jogging when there's maths like that.
    Last edited by pete; 03-24-2020 at 10:55 AM.
    bored, curious, deaf or just bad taste in music?
    finally a mix by me
    and what's this, another shoddy mix...another dull mix

  3. #3
    Moderator pete's Avatar
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    bonus points: spot how many times one of the best techno DJs ever (Jeff Mills) has to adjust his mixes when the beats start slipping.

    bored, curious, deaf or just bad taste in music?
    finally a mix by me
    and what's this, another shoddy mix...another dull mix

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    Quote Originally Posted by pete View Post
    Maths.
    that thing at school that was boring.

    Lets look at 3 cases:

    [1]

    Track 1 is 133 BPM
    Track 2 is 137 BPM

    To match them together I need to reduce the speed of track 2 by 137/133 =1.030075187969925% exactly. ish.

    Being a full-on jedi DJ, I can match these up no problem by measuring the amount of atoms on my pitch fader and adjusting correctly.
    Or just guess and keep them in time by adjusting the pitch fader and platter every now and again so no one notices. the maths.

    And even so...if I get the track to 1.04% that means that it will slip out of time by about 1/10000 of a second for every that passes second. So 10000 seconds to slip out of time by one second. Which is just a bit more than 1 beat at the 133BPM I'm rocking the crowd at. 10000 seconds is 2.78 hours. Aint no dancefloor got time for a track that is 2.78 hours!

    So basically its ok to slip a bit and adjust as you go along.
    Unless you're Carl Cox. Then if you slip a bit then everybody gonna be over you saying that you aint no longer the 3 deck wizard. HOLY JESUS.

    [2]

    Track 1 is at 130 BPM
    Track 2 is at 130 BPM

    Both are pitched up by 4%. Because as every DJ knows, everything sounds better at +4.

    Now on old analog turntables this would be an issue, cos to get both pitch sliders at exactly 4% is a mathmatical impossibility (as we looked at in case 1).
    The only way to get them really close would be to play the tracks at 0% and have the Quartz-lock light on. Because quartz lock makes you a mixing magician where all tracks at the same BPM mix together perfectly. You can call yourself the "quartz-lock warlock" or something,. (but even quartz-lock is subject to maths, so you gonna have to touch the decks a bit...). Math is a b!tch. Or rather you're maths's b!tch.

    On your fancy-pants DVS system, in theory this should not be an issue. Tracks should be locked at the same exact tempo. Both locked at 4%, both locked at 135.2BPM. Because maths. I should be able to go and get a beer and enjoy some sweet pleasure with the groupies and still be holding down a mix like some sorta blending Chuck Norris.

    However, if there is any I've learned in my decades of DJing....nothing about DJ equipment is certain (apart from maths). The only way I have to combat this is to be totally certain of my beatmatching skills. I have to be absolutely sure that even in the caldera of an erupting volcano whilst being pleasured by an army of over-eager valkyries, with belt-drives and broken headphones....I can match 2 tracks in less than 2 seconds.

    Anyways DVS has sync. They didn't invent that by chance. It aint a crime to use it. Unless the DJ Police are around.

    [3]

    You're a famous international DJ/Producer.

    It's all good cos you're playing a premixed CD.

    Even after a while when you've grasped the concept of a mixer, someone has time-stretched all your tracks to 128BPM so you just have to flip the fader over with one hand, and wave like the Queen with the other.

    After all its a 100000$ show, aint no one got time for pitch wheel jogging when there's maths like that.



    Wow, thank you for our insight Pete

    So what you're essentially saying if I've understood correctly, is that it's basically impossible to manualyl adjust two tracks to be prefectly in sync with eachother BPM wise. This can only be achieved with the ol' sync button. So constantly correcting is an innevitable part of mixing, again, unless using sync. I still am a little confused as to how the two tracks I was messing around with earlier were unsyncing so fast, with such a a seemingly marginal % difference.... But hey ho!

    I must have just been hanging out with too many DJ po-po's! Cause I've always been under the impression that syncing is looked down on. Don't get me wrong, I use it a lot! But I figure whilst I've got so much time on my hands, might as well learn how to do it the original way? Do you have any further tips on how best to learn to beatmatch? I'm currently working my way through Youtube tutorials on the matter...

    And yes, good point about Jeff Mills! That video looks sped up he's movign so fast... damn.
    Oh yeah and could you please explain what you mean about the 4% pitching up thing??

    Cheers buddy!

  5. #5
    Hammerite Manu's Avatar
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    Quote Originally Posted by devs View Post
    if I've understood correctly, is that it's basically impossible to manualyl adjust two tracks to be prefectly in sync with eachother BPM wise. This can only be achieved with the ol' sync button.
    Absolutely not. I never used sync, but I have no problem beatmatching and get a lock most of the time. While you may get the odd slight drift, that's what adjustments are for when beatmatching.

  6. #6
    Deez Beats! KLH's Avatar
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    Just to add to the thread, the objective isn't usually to maintain synchronization between sound sources for a long time. The objective is to have them be well matched enough to transition between them. As such, maintaining sync for a long time generally isn't needed.
    -KLH
    Visit DJF's Beginner's MEGA thread and drop by my Facebook Fan Page.

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    Moderator pete's Avatar
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    Quote Originally Posted by devs View Post
    Wow, thank you for our insight Pete

    So what you're essentially saying if I've understood correctly, is that it's basically impossible to manualyl adjust two tracks to be prefectly in sync with eachother BPM wise. This can only be achieved with the ol' sync button. So constantly correcting is an innevitable part of mixing, again, unless using sync. I still am a little confused as to how the two tracks I was messing around with earlier were unsyncing so fast, with such a a seemingly marginal % difference.... But hey ho!

    I must have just been hanging out with too many DJ po-po's! Cause I've always been under the impression that syncing is looked down on. Don't get me wrong, I use it a lot! But I figure whilst I've got so much time on my hands, might as well learn how to do it the original way? Do you have any further tips on how best to learn to beatmatch? I'm currently working my way through Youtube tutorials on the matter...

    And yes, good point about Jeff Mills! That video looks sped up he's movign so fast... damn.
    Oh yeah and could you please explain what you mean about the 4% pitching up thing??

    Cheers buddy!
    While mathematically impossible to tempo-match "perfectly" some if not most tracks together using analog equipment, it is very possible to mix them in a way that is imperceptible to the human brain to discern any beat-slippage.

    Technically using digital equipment it should be possible to mix some tracks dead-on perfectly (where the maths divides dead-on with your pitch range incrementation). If the track was made with digital equipment that had perfect tempo, and your equipment holds perfect tempo. There's bascially no reason why it shouldn't work.

    Sync uses the computer's power to try to match the beats as best as possible. It aint perfect, but usually it works OK..

    So sync is looked on badly, but its been a while. As long as you know proper beatmatching, it aint a crime. If you are a n00b with a ton of stolen music and a sync button on a controller, its always going to look bad against old-school DJs, and brings the scene down generally.

    As for +4% ... that's just the way we used to play. Uptempo gives the track more energy.
    bored, curious, deaf or just bad taste in music?
    finally a mix by me
    and what's this, another shoddy mix...another dull mix

  8. #8
    Good question.

    I've been trying to source faders and according to spec sheets they can have as much as +/-20% tolerance depending on the manufacturer.

    Now, your computer does the voltage calculation (or the turntable manufacturer did the pitch calibration for you but certain mechanical/electrical conditions etc may cause fluctuations) since the MCU works by reading the voltage from the controller, ie. a potentiometer or a fader. I can already tell you that the ICs in controllers etc are much like the commercially available FPGAs, the problem with prototyping is the breadboarding which introduces stray capacitance due to the design (many breadboards have the rails shorted with jumper bits), in other words the final circuit could be more stable as it's soldered (another thing is how and with what type of electricity and PSU it's powered with once it's assembled as they're usually prototyped "in vitro")

    Technically you're giving the pitch fader a 5VDC input and the MCU that receives the control voltage transforms the values into pitch/speed changes, ie. it's designed to respond to the voltage changes you do. In theory, with an ideal power supply in a 5V system 2,5V is the 0% but for example a 10bit MCU tracks the voltage within a 0-1023 range so you have 5mV accuracy (it gives you 512 different values both ways so in a +/-10% pitch range you get 0.02 increments) but this doesn't account voltage spikes or sags (you can try this with a microcontroller by hooking up 5V to a pot which feeds an analog input pin and establishing a serial connection to track the potentiometer values via serial monitor)

    As to how the software deals with the pitch/speed is another thing.. if I was to guess it clocks the memory bits where the data is read from (with slow playback speeds and files with low sample rates this is perceived as the sound becoming grainy due to the gaps that form between individual samples)

    In contrast with faster playback speeds it results in information being lost.

    Now, the human auditory system can detect very subtle changes in the stereo field (or the relation of two sounds coming from the same source, in a normal case the kick drum) and given the system I explained earlier with 120bpm (2 beats per second) using a +/-10% pitch speeds up or slows down the song by 1bpm with roughly +/-0.80% which means a single increment could cause a 1/16bpm (in a 0.05% pitch) or 1/32..40bpm shift which I quickly calculated as 30ms since 1bpm change in 120bpm is ~500ms, divided by 16 (notice I don't have CD players with 0.02% pitch, mine are 0.05%)

    I remember reading a research which suggested that the human brain is able to distinguish differences in auditory field by 15ms (for comparison a studio slapback delay can be close to 30-50ms) but phasing is a phenomenon which is perceived as two signals cancelling each other.

    This happens if you play the same track from two sources, which is when electronic interference, fluctuations and component tolerances, cable lengths etc come into play, you wouldn't normally notice it with 2 different tracks and most DJs use EQ to cut the bass.. it may also be noteworthy that the average physical response time of a normal person is 1,5..2 seconds.

    And all this is done in an ideal, "free-space" environment where room acoustics aren't taken into account (it's very different in headphones though where you may be able to notice these things before they come out of the speakers)

    Early mixing engineers made use of the phenomenon by recording a signal into 2 separate tape reels and physically speeding up or slowing down the other one.

    Some people hinted it could be possible with digital equipment.. which is true in theory but in practice they would fall out of phase, unless you have laboratory-grade equipment and even then you'd probably be hard-pressed to keep them in sync.

    Another thing was if you mixed deck A in the left ch and deck B in the right or vice versa and had the opportunity to position the speakers and the audience precisely (this is also a mixing trick used to create an artificial stereo image)

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