easy scratch machine for dj??

[swt]

HI. i just want to make a scratch machine for the noisemaker in my band. is there a way to simulate this with electonics?. or should i buy a cheap disco pick, amplify it with a booster, and use a pad as a surface, or old disco, and then to fxs?.
And what about a static noisemaker...like old disco static?. thanks a lot!!

[Antero]

A turntable?

[jonathan perez]

toggle gating:

3 way switch-2 pickups-2 volume controls

one pickup volume full up, the other all the way off.

while toggling between the on pickup, and the off pickup, use your free hand to rub the strings around the pickups to create a scratching  sound. %^&* a wah and add delay for further menace.

[Pushtone]

How about a volume pedal with an intentionally scratchy pot.

Take a pot and rub it in very fine sand, talc, coffee grounds, whatever makes a nice scratch sound when turned.
Mount the pot in a wah shell. Add active circuit, buffer, booster, etc.

Voice the circuit to roll off bass and make it sound the way you want.
Maybe add a resonance filter to emulate the program music on the vinyl.

The tough part will be the voicing. Scratching a record produces a "zip" sound. Scratchy pots more of a crackle.
DSP and sampling would produce a more realistic sound but it would be cool if a simple DIY approach created a workable sound.

Good luck

[jonathan perez]

tape recorder (play mode)+humbucker=noise?

[Pushtone]

That reminded me of Lori Anderson and her magnetic tape violin bow


She recoded audio onto 1/4 magnetic tape using a ancient device know as a reel-to-reel recorder.
She attached some of the tape to a violin bow in the fashion horse hair would be attached.
She had mounted a playback head from a cassette player on the violin bridge.
Instant performance art.

Battleofthemidway and Lori's concepts can be combined and applied.

A magnetic scratch pad, held in the strumming hand and used to modulate the pickups and or strings.

[sfr]

That reminded me of Lori Anderson and her magnetic tape violin bow


She recoded audio onto 1/4 magnetic tape using a ancient device know as a reel-to-reel recorder.
She attached some of the tape to a violin bow in the fashion horse hair would be attached.
She had mounted a playback head from a cassette player on the violin bridge.
Instant performance art.

Battleofthemidway and Lori's concepts can be combined and applied.

A magnetic scratch pad, held in the strumming hand and used to modulate the pickups and or strings.

That is so cool.  I was contemplating a vaguely related concept a while back, but figured it wasn't actually something that would work.   Now I may have to revisit it.  Thanks for sharing that.  I was totally unaware.

[Mark Hammer]

Scratching is produced by a prerecorded piece of audio signal (usually vinyl disc) being: a) played forwards and backwards at speeds that are b) subject to acceleration and decelleration, and c) much higher than the speed at which the signal was originally intended to be played.

Seems to me that the most convincing way to produce "scratching" in the analog domain might be to have a series of cascaded decade counters with their outputs pooled to a mixer stage.  What the "scratch hand" does is to control a 555-based clock that steps the counters through their sequence.  As the clock rate accelerates, the apparent pitch goes up, and as you slow it down, you get the "braking" action. 

For more realistic scratching, you want to be able to have silence on demand.  For that, I imagine a setup like the following might work.  Let's say you have a "platter" as the knob of the clock-speed pot (indeed this is what they have on some cheap keyboard with "scratch capability").  You can decide on what diameter suits you, but something in the range of a 6" disc might work.  What is key here is having a momentary switch underneath the mechanism such that as you go to press on the disc, you actuate the sound.  The sound itself can be actuated by either connecting the clock to the first of the cascaded counters, OR by connecting the summed output of the counters to a subsequent audio stage.  I.E. you hear nothing until you press.

The most problematic thing about this imaginary design, I suppose, is determining just how many counting stages you need to yield a discernible and useful sound.  The counters CAN be rigged to loop back continuously from the end of the count such that they form a kind of continuous waveform generator.  The nature of the waveform generated is determined by which of the counter-sequence outputs are fed to the mixer and in what proportion.  Non-fed outputs are functionally equivalent to negative half-waves, while outputs fed through are equivalent to positive half-waves.  If you simply fed every second output to the mixer as is, you'd have nothing any different than a simple square-wave oscillator.  The counters provide an advantage in that you can "construct" an irregular waveform that can be set to bear some remote resemblance to a musical signal rather than just a continuous tone by using something other than an alternating sequence and partially attenuating select counter outputs.

Another approach is to use something like what was used in the ETI Cymbal synthesizer.  Here, CD4070 Exclusive OR gates were used to create digital (well, CMOS anyways) ring modulation.  The production of sidebands (especially when you pooled the outputs of two ring modulators into a third one) dramatically increases the number of "elements" in the final audio output.  Remember that "real" scratching consists of imposing drastic acceleration and decelleration on a rich complex prerecorded signal, so generation of a multi-pitch signal incorporating many elements might be just the ticket.  I know the schem is posted somewhere on-line but can't quite find it at the moment.  I have it at home and will see if I can post the critical portion of the schem to illustrate.

Does any of this make sense?

[choklitlove]

it's processing...

i'll get back to you in a day or so.

[swt]

wow thanks a lot for all your answers...seems like there are some good ideas around, but at the end guess an old turntable will be easier to have, right??

[jonathan perez]

i used to DJ, and i think theres NOTHING wrong with adding a turntable to your rig...under the condition that its hidden underneath a beer case or something...

[Mark Hammer]

Like I say, there ARE inexpensive keyboards that have a built-in scratch function.  Yamaha made one and so did Casio, IIRC.  Both those puppies ought to be sitting in one of the many garage sales on in your neighbourhood now.

[Arn C.]

Get one of those little kids phonos at a yard sale.   May look cool on stage and also it will be smaller, easier to bring with you !

Peace!
Arn C.

[jonathan perez]

and what to use to simulate the cross fader?

[sfr]

You know, I can get a decent "scratch" effect with a delay pedal that's oscillating/infinite repeating - having a kill switch, and a toggle to double to repeat times down there makes it even easier.  I have a recording of my band somewhere where I do something similar at the end of a "freakout" during the last bit of the last song of the set, using guitar feedback, the HOG, and a PT-80.   I manage to make it sound somewhat like scratching and a drum machine.  I'll see if I can't find it.  Of course, it's one of those things that's difficult to repeat consistantly.

[mars_bringer_of_war]

toggle gating:

3 way switch-2 pickups-2 volume controls

one pickup volume full up, the other all the way off.

while toggling between the on pickup, and the off pickup, use your free hand to rub the strings around the pickups to create a scratching  sound. %^&* a wah and add delay for further menace.

Straight out of Tom Morello's playbook.
Works well, actually.