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About reverse action

I was browsing thru this other forum and spot this:

"you wanna keep the mix seamless... pushing or slowing any part of the technics platter will cause reverse reaction due to platter compensation... this will screw your mixes (unless you know you can compensate back what the platter has done - and this can be done by pitch blending"

Not knowing whether this guy is theoriatically rite or not, i found it so very true. Tho i am not using technics, i am spinnin on two TT-200 decks, and this happens to me a lot and hell it pisses da shit outta me. my question is, does the this REVERSE actioni true or is it just my ear and not good enuf yet.... ??

i think what he's saying is that lets say you push the record forward, the platter is moving at a constant speed so it "reacts" by slowing the record down to its normal speed (although the platter is always moving at more or less a constant rate)

Watch the dots...

I've noticed this on my TTX1. The way to see if it's happening is to put the pitch on 0%, slow the record down slightly while watching the dots moving backwards, then release the record. I find that the dots overshoot slightly when returning to stationary, as in they don't just stop dead when you let go the record, they overshoot by about 5mm.

This is probably to do with trying to combat friction and having an accurate pitch setup -- they use a closed loop control system which is set up to counteract any slight friction forces, say in the spindle or bearings.

It's a bloody difficult problem to solve if you think about it, how to make a turntable keep constant pitch over its life while taking into account bearing friction, and still not overcompensating for a DJ giving the record a little tweak... I guess it comes down to tweaking the DJ, not the gear

Get a CDJ! It doesn't overshoot!

Re: Watch the dots...

quote:

Originally posted by nebbian I've noticed this on my TTX1. The way to see if it's happening is to put the pitch on 0%, slow the record down slightly while watching the dots moving backwards, then release the record. I find that the dots overshoot slightly when returning to stationary, as in they don't just stop dead when you let go the record, they overshoot by about 5mm. This is probably to do with trying to combat friction and having an accurate pitch setup -- they use a closed loop control system which is set up to counteract any slight friction forces, say in the spindle or bearings. It's a bloody difficult problem to solve if you think about it, how to make a turntable keep constant pitch over its life while taking into account bearing friction, and still not overcompensating for a DJ giving the record a little tweak... I guess it comes down to tweaking the DJ, not the gear

Very well said mate.

Here is where the arguement for using the pitch sliders to beat match rather than hands on platter rears it's ugly head again. But I have been saying for some time now and people have been telling me it's crap, but I know it's not!

Although it's harder to do, you are better off learning to use the pitch control. It takes time but it is worth it. And your corrections become less offensive (Assuming that you can hear them at all).
Definately the way to do it in my humble opinion.

Cheers
Nem

Nem gets his asbestos body armor out again.

quote:

Originally posted by Nemesis44 Here is where the arguement for using the pitch sliders to beat match rather than hands on platter rears it's ugly head again. But I have been saying for some time now and people have been telling me it's crap, but I know it's not! Although it's harder to do, you are better off learning to use the pitch control. It takes time but it is worth it. And your corrections become less offensive (Assuming that you can hear them at all). Definately the way to do it in my humble opinion. Cheers Nem Nem gets his asbestos body armor out again.

Yep I think the pitch control is the best method besides of this compensation thing that decks have. Plus I think it's faster just pushing the pitch slider up and down till you find "the spot". What I don't like about the pitch is since it doesn't have a visual display like a CDJ, you have to pitch-ride the mix after your first "live" correction which is a pain
but that will come with practise I guess, as usual

it is true. i think i have posted this once somewhere but it has to do with magnetic induction. i think this is how it works...

if you apply force on the platter, the magnet induces a current. a change in current induces an opposing force. so you have two opposing forces...it acts like a spring.

on the turntable you can change the voltage which i guess would change the damping constant of the harmonic motion so that its critically dampened and doesnt fire back at you too much. i havent exactly figured out exactly how but i think its on a blue pot thats on the underside of the pcb that the pitch fader is attached to.

as for the pitch riding...yes the pitch is probably technically the smoothest way to go but going back to the dampening... i touch the platter with my finger and when its on beat i slowly and lightly let it go. i dont just take my finger off...i try to simulate my own dampening to counter the force that is trying to snap the platter back to speed.

quote:

Originally posted by DjJade it is true. i think i have posted this once somewhere but it has to do with magnetic induction. i think this is how it works...

Damn you! I wanted to say that and sound clever! But seriously, this is absolutely correct. The reverse force you exert on the motor induces a current into the coils, and the induced current is in the opposite direction to the acceleration of the motor (deceleration, i.e. slowing down the platter, is actually an acceleration, just in the opposite direction). Therefore, when you stop slowing down the platter, the current you have induced forces the motor to be faster than the original speed of the motor for a short time, and it then goes back to its original speed.

Try out the pitch fader method... its not that difficult once you get used to it, and it does make the mixes sound smoother, especially if there are vocals. You try playing a vocal track and slow down the platter and releasing it. I guarantee it will sound awful.

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