O-SCOPE XY mode

[igor12]

How does one use the XY mode for something related to audio electronics?

[BrianJ]

I think it can be used for phase alignment.  I belive thats the mode used for checking the "azimuth" (sp) of a tape machine's heads. 

I never really go there myself so I can't help much more than that.

[pjwhite]

Back in the days of vinyl disc production, mastering engineers would run left and right audio channels into the X and Y scope inputs to monitor the waveform, watching for vertical modulation.  A mono signal would produce a mostly flat line (at 45 degrees).  A normal stereo signal would wiggle around a bit, but generally stay along this 45 degree line.  When low frequency  signals went 90 degrees out of phase, the disc cutter would be moving the cutting head up and down, more than left and right, and the resulting record would make the needle jump up out of the groove and cause skips.

[Ge_Whiz]

It's indeed commonly used to check phase relationships, but you can connect separate signal generators to each input and make cool Lissajous figures on the screen - very '60s Sci-Fi film effect.

[The Tone God]

I use it to check phase changes through various amplifier stages. I also use it to check propagation delays in digital circuits.

Andrew

[George Giblet]

A very common use is to get a straight line which indicates the two signals are in phase.

You use this when you are trying to find the resonant frequencies of circuits (or systems).   One example is you construct a resonant circuit with with an inductor and a capacitor: you find the resonant frequency, then if the capacitor value is known you can find the unknown inductance.  Another use is finding the resonant points of the impedance of speaker systems which then allows you to determine certain speaker parameters .

There's also RF applications, this is quite a good example:
http://www.icycolors.com/nu9n/scope_your_audio.html

Basically it is a tool that you can use in innovative ways to measure or see things which would otherwise be difficult on the time-based display.

[Ronsonic]

You can look at phase relationships as mentioned and you can view noise plus distortion.

Ron

[igor12]

Thaks for the resposnses. So I can hook up a sine wave to ch1 and a different sine wave to ch2, put scope in XY mode and see some cool shapes? If I very the frequency so that both are almost the same but slightly out of phase, will I see a straight line? Ya know what I'm gonna in the basement and play.

[guitar_199]

Think of it like an "Etch-a-sketch"

One knob, the up-and-down, is like the Y channel, the other knob is like the X channel.  Start by putting the dot in the center, then shake the etch-a-sketch to clear it.

Now, if you put a hand on each knob and make the x and y go up at the same time you get a 45 degree line going from the center to the up-and-right.  Reverse the direction of both hands simultaneously ( and ACCURATELY) and the movement will reverse and go 45 degrees to the down-and left.   Repeat this rapidly and you have a 45 degree line from lower-left to upper right.

If you go up on the x while going down on the y the same rate, you will have a 45 degree line from the upper left to the lower right.

If i recall correctly ( and I MAY not...its been a while) phase differences and frequency differences create open elliptical shapes and  various multiple loop images that are a) predictable and, b) can be used to tell you what the phase/frequency difference is.

[Ge_Whiz]

Thaks for the resposnses. So I can hook up a sine wave to ch1 and a different sine wave to ch2, put scope in XY mode and see some cool shapes? If I very the frequency so that both are almost the same but slightly out of phase, will I see a straight line? Ya know what I'm gonna in the basement and play.

No, wwwwaaaaaaayyyyyy cooler than straight lines!