Stereo thoughts

jammers

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Joined
Jan 19, 2005
Anyone use those stereo effects processors for vocals or anything? Found me self a cool way to achive the same effect, but without the cost of buying a processor! make yourself a splitter cable (1x female xlr- 3x male xlr), plug the input you want to use this effect on into the F-xlr then plug the M-xlr into three channels on the board. Use, say, channel one as you would normally then with ch2 and 3 pan them hard L(ch2) and R(ch3) and hit the phase switch on both. Bring em up after you have set ch1 and it will give you a cool stereo imaging effect!

Just a thought as the 'audio tips n tricks' seems to be abit slow.
 

Andy_Leviss

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Dec 26, 2004
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Sorry to burst your bubble, but this won't work. The left and right are exactly the same, not to mention that all you're doing is effectively reducing the volume by cancelling out half of the signal, since you're sending the exact same signal with reversed polarity (it is NOT, NOT, NOT a phase switch, it is a polarity switch; reversing polarity effectively throws the signal 180 degrees out of phase, but they are not really the same thing).

Ch. 1, panned center, is sending 50% of the signal to L and 50% to right.

Ch. 2 is sending 100% of the signal with reversed polarity to L

Ch. 3 is sending 100% of the signal with reversed polarity to R

This means that L is getting 50% of the original signal plus 100% of the reversed polarity signal, which means that, when you add the waveforms together, it's really getting 50% of the reversed polarity signal.

The R channel is getting exactly the same thing.

So, not only are you not getting anything remotely resembling pseudo-stereo, but you're throwing away half of your level.

Not to mention that, in live audio, 9 times out of 10 when people think they're running a stereo system, they're really running a split-mono system, so trying to do a stereo effect is pointless. No, actually, it's less than pointless, it's detrimental.

If you don't have a full L cluster with a mix of short, medium, and long throw cabinets that can cover the entire venue at an equal level on its own, without the R, and the same on the R side, you DO NOT have a stereo system. If you insist on running stereo signal through such a split-mono system, the majority of your audience will miss most/all of one side or the other.

--Andy
 

jammers

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Joined
Jan 19, 2005
yeah my mistake on the phase switch, the way to do it way flip the signal on the cable. I was not talking bout doing in live sound - but i can be cool in the studio if used right! That is the basic way the lower end stereo processors work.

Anyway i do hear you on the dual mono point, there are only afew systems that i have worked on that could be called true stereo, you then can start to mix with that as a handy tool!
 

jammers

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Jan 19, 2005
Anyways try the stereo thing, i got taught it many years ago from a turbosound r+d engineer, ive used it a couple of times when doing studio work (mainly when in the lower quality ones without the nice fancy gear)
 

Andy_Leviss

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Dec 26, 2004
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NYC
Flipping the signal on the cable is THE SAME THING as hitting the polarity switch (again, stop calling the thing a phase switch, it's NOT).

Again, you're still doing the same thing to both channels, so not only is it not doing anything w/r/t stereo imaging, it's cancelling out much of your signal.

Sorry, but you can't change the laws of physics. And, beyond that, common sense tells me that if I do the same thing to two different signals, no matter what it is that I do to them, those signals are going to stay the same, and thus not in any way, shape, or form resemble a stereo effect.

Basic stereo simulation involves shifting the phase, yes, but NOT 180 degrees, and most certainly NOT IDENTICALLY ON BOTH CHANNELS. If you want a pseudo-stereo effect on the cheap, you'll have more luck by splitting the signal to two channels, and delaying one by 20 ms or so.

It's really just basic physics, this isn't anything complicated.
 

Andy_Leviss

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Here is a tutorial from SOS magazine on how to create pseudo-stereo that explains it properly, and is probably where you're getting confused, since it DOES involve flipping polarity, but also a LOT more steps and only doing so on ONE channel. (Do note that this guy also misuses "phase" when what he really means is "polarity".)

The basic approach to creating a useful and reliable stereo effect from a mono source that remains mono-compatible is based on using Middle and Sides (M&S) techniques. Consider the mono source as the M signal, to which we need to add a 'fake' S signal. The resulting pair will then need to be decoded back into left and right for mixing into the stereo track, of course. The advantage is that the S signal disappears in mono, so the original source track remains undamaged for the mono listener, and hopefully usefully enhanced for the stereo listener.

At the most simplistic level, the primary difference between the M and S signals is time. Imagine a source in front of an M&S mic: the direct signal reaches the M mic, while the same signal has to travel to and bounce back from a wall to reach the sideways-facing S mic. Consequently, all we need to create a useful fake S signal is delay the original by a small amount: a simple mono delay line is all that's required.

Take the source, split it in two and route one to the centre of the stereo output, and the other to a delay line. In practice, I like to pass it through a high-pass filter first and roll off the bass below about 150Hz, as I find that produces a better effect; it can become bass-heavy on the left channel if you don't do this, depending on the source material.

The secondary M signal is routed through a high-pass filter and into a delay line. The minimum delay I would use is about 7ms, extending up to about 25ms, but feel free to experiment. With classical music, you could go as high as 80ms to create a kind of symphonic hall effect. Changing the length of the delay changes the character of the stereo effect. The output of the delay line is the fake S signal, and this now needs to be combined with the M signal to decode back into stereo.

Split the output of the delay line into two signals and phase-invert one of them. Route the normal output to the left channel mix buss, and the inverted one to the right channel mix buss. Ensure that the amount of +S is exactly the same as the amount of -S, so that when summing left and right channels in mono you cancel the S signal completely: (S+(-S))=0.

The easiest way to do this is to route the two S signals through a stereo fader, which also allows you to control the apparent width of the stereo effect — but don't go mad. The result can sound impressive, but it gets tiring quickly, and the mono and stereo mixes will sound radically different if you add too much.

Hope that helps. This technique is used very widely in broadcast post-production and in mastering when 'up-converting' archive mono to stereo, or stereo to surround.
 

avkid

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Feb 17, 2004
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Lakewood, NJ
Here are some dictionary definitons for you guys:

Phase:
In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i.e. density, crystal structure, index of refraction, and so forth.) The most familiar examples of phases are solids, liquids, and gases. Less familiar phases include plasmas, Bose-Einstein condensates and fermionic condensates, strange matter, liquid crystals, superfluids and supersolids and the paramagnetic and ferromagnetic phases of magnetic materials.

Polarity:
Polarity is a term used in electricity, magnetism, and electronic signaling. Suppose there is a constant voltage, also called an electric potential or electromotive force (EMF), between two objects or points. In such a situation, one of the objects or points (poles) has more electrons than the other. The pole with relatively more electrons is said to have negative polarity; the other is assigned positive polarity. If the two poles are connected by a conductive path such as a wire, electrons flow from the negative pole toward the positive pole. This flow of charge carriers constitutes an electric current. In physics, the theoretical direction of current flow is considered to be from positive to negative by convention, opposite to the flow of electrons.
 

Andy_Leviss

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That is the entirely wrong definition of "phase" for what we're referring to. Audio signals, and other waveforms, do have phase. However, pressing the button on your console doesn't do anything to that phase. It does, however, invert the polarity, which produces an identical end result to a signal that is 180 degrees out of phase.

The definition you're looking for for "phase" is, "The fraction of a complete cycle elapsed as measured from a specified reference point and often expressed as an angle." Or, from another source, "Angular relationship between two waves." (Both of these found at: http://www.answers.com/phase&r=67)
 
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The basic approach to creating a useful and reliable stereo effect from a mono source that remains mono-compatible is based on using Middle and Sides (M&S) techniques...
The teqnique described here is an adaptation of the Stereo MS Micing technique (which involves getting a stereo signal from a cardoid and a bi-directional mic). It's all in the math unfortunatly, I'll reply to this tomorrow once I'm slightly less intoxicated and go through it, but the basic principal behind an MS decode is:

(x+y)+(x-y)=2x
(x+y)*-(x-y)*=2y

2x/2y = x/y


*Note the need for a polarity flip to make the equation between the asteriks work out properly.
 

BNBSound

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Mar 17, 2005
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Alexander, NY
Ya know... if you really wanted to generate a stereo phasing effect, you can pick up a Nanoverb on eBay for around forty bucks. Then you're only gently massaging the signal instead of haiving it drawn and quartered and thrown to the winds.