Check out this little trick I discovered!

[Thunderbolt1000T]

I don't know if anyone else has discovered this yet, but there is a way to further spread out a stereo recording in Audacity. This is a neat little trick I discovered while experimenting with the Invert effect, and it has been very useful for me on multiple ocasions. This produces the same effect as the SRS Wow effect in Windows Media Player, or the "Surround Sound" button on some boom boxes. I recommend using the Amplify effect to lower the audio to about -7 DB before starting, to prevent clipping, and I also recommend listening through headphones while trying this out.

1. Record or import the audio you wish to spread out. It must already be a stereo recording.
2. Copy the original track by pressing Control+C.
3. Create a new stereo track, and paste the coppied audio into it.
4. With only track 2 selected, go to the Tracks menu, and select Stereo to Mono.
5. Apply the Invert effect on the now mono track 2.
6. Mix and render tracks 1 and 2 into a single track.
7. Create a new stereo track, then press Control+v to paste the original audio you copied earlier into it.
From here, you can mix and render if you like the way it sounds, or you can adjust the gain on each of the two tracks to spread the two channels out the desired distance. Also, if you want to bring the two channels closer together instead of spreading them out, you can invert track 1 at this point, and you should get a mono signal if the gain on both tracks is the same. From there, you can turn down the gain on track 1 to make the signal stereo again, and to get the desired effect.

If a plugin hasn't been created to do this yet, I'd like to see one made, but I'll leave that up to the experts, because I don't have a clue how to make a plugin. Please try this little trick out and tell me what you think!

[billw58]

Plugins that will do this are the "stereo butterfly" effects available here: http://audacityteam.org/download/nyquistplugins.

After your step 6 you have a new stereo track where the channels are flipped and inverted compared to the original. That is:

L' = -R
R' = -L

Mixing these with the original results in:

L'' = L - n*R
R'' = R -n*L

Where "n" is the gain setting on the flipped and inverted track.

-- Bill

[kozikowski]

At the end of step six you have a top to bottom arrangement of this:

-R
-L
+L
+R

You can get there by applying Invert to the original top track and applying the Left and Right split reversal tools in the track menu under the black arrow to the left of the track. Fewer steps.

There are one or two more rules to this. In the mono mix you get (-L-R) and (-R-L) -- double the size of the two original signals. This could overload if you're not careful. For example, the stereo orchestra can easily be manipulated like this, but the singer in the middle (she appears the same on both left and right) might have overload problems, since she doubles in volume.

Correct me, but you can also get there by leaving the first track alone and inverting/splitting/reversing the second track.

+L
+R
-R
-L

In which case you would have invented Stereo FM.

Koz

[steve]

If a plugin hasn't been created to do this yet, I'd like to see one made,

For the specific case of widening stereo there is as Bill has said, the "stereo butterfly" effect.
For a more versatile effect there is the "Channel Mixer" plug-in here: http://forum.audacityteam.org/viewtopic ... 39&t=33563

[Thunderbolt1000T]

You guies are wrong about what the results should be after you mix and render in step 6. You should get l=l+(-r,) and r = (-l)+r, where -l and -r = inverted l and inverted r, respectively. If you try to play this mix through a set of mono headphones, you'll get absolutely nothing, because the two sides will cancel each other out. However, if you play it through stereo headphones, you'll get what sounds like a sort of stereo version of Vocal Remover. If you combine this stereo mix with step 7, it does absolutely nothing to the volume on the center vocal, but it does increase the volume of the left and right instruments, resulting in a more spread out stereo mix. Because of the volume increase on the right and left instruments, I recommended in my previous post to use the amplify effect on the original audio before starting, to lower the audio to -7 DB, so you'll have some leeway for the volume increase. If you forget to perform step 7, you'll just end up with the inverted and non inverted versions of what the vocal remover does, which is not what you want. You have to paste the contents of the clipboard back into a new stereo track to get the "SRS Wow"-like effect. If anyone wants me to post audio examples, I can post them.

Edit: Steve, your plugin does exactly what I'm talking about without all those steps! Thanks!

[billw58]

Right you are. That's what I get for thinking about that too early in the morning.

There's a factor of two in there that I neglected.

After step 5 you have:
a) A stereo track consisting of channels L and R
b) A mono track that has the equivalent of stereo channels each being -(L+R)/2
(The factor of two is applied within the Stereo to Mono command, otherwise the resulting waveform could reach + 6dB)

After step 6 you have a stereo track with channels:
L' = L - (L+R)/2 = (L-R)/2
R' = R - (L+R)/2 = (R-L)/2

Finally when you mix the rendered stereo track with the original, and vary the gain of the rendered track, you get

L'' = L + nL' = L + n(L-R)/2 = (1+n)L - nR
R'' = R + nR' = R + n(R-L)/2 = (1+n)R - nL

-- Bill

[steve]

2. Copy the original track by pressing Control+C.
3. Create a new stereo track, and paste the coppied audio into it.
4. ...
5. ...
6. ...
7. Create a new stereo track, then press Control+v to paste the original audio you copied earlier into it.

These three steps can be done more easily by using Ctrl+D (duplicate track).
but of course using the Channel Mixer plug-in is even quicker and easier (especially if you use one of the presets).

[Thunderbolt1000T]

Hey Steve, I have a question about your plugin. How do I get an exact duplicate of what I get doing it manually? I've noticed that the Wide Stereo setting isn't quite as wide as what I get manually, and the Extra Wide setting is way too wide for my tastes. What custom settings should I use?

[steve]

How do I get an exact duplicate of what I get doing it manually?

There was one area of "vagueness" in your description: "From here, you can mix and render if you like the way it sounds"

So what is the exact "formula" of your method?
For the new Left Channel: How many % of the old Left Channel? How many % of the old Right Channel?
For the new Right Channel: How many % of the old Right Channel? How many % of the old Left Channel?

In the Channel Mixer plug-in, negative values represent inverted signals, so for example, "50% of the old Left Channel and 25% of the old Right Channel inverted" would be achieved with settings of "+50 and -25".

If you click the Debug button to apply the Channel Mixer effect, the exact "formulae" are printed to screen after the effect has been applied.

[billw58]

The advantage of the OP's method is that you can vary the gain slider on the rendered track until you get the effect you want, then mix and render everything. With the Channel Mixer you'd have to choose some settings, apply it, then undo and try again if you didn't like it. Of course, once you find a setting you like you can quickly apply it to other tracks.

If my math is (finally ) correct, you have to be careful when translating gain settings for the rendered track into your plug-in.

Because L(new) = (1+n)L - nR

if the gain setting was e.g. -6dB, then n = 0.5, and

L(new) = 1.5L - 0.5R

then the factor to apply in your plug-in would be -33% to get the same effect.

Right?

-- Bill