Gotta widen some tracks, and add width to an old mix that was transferred from a cassette, and looking for some recommendations.

Channel Tools. 

Within Sonar my vote goes to Channel Tools.  Don't know how this will work with an entire mix though.

Im with the others, 

I like Channel tools and the Extra Ambience Preset then adjust out from there

Ozone also has a widener. 

There are widening plugs. Some are OK some not so much. 

If live recording, double the track   of  the acoustic guitar by recording it 2 times and pan it wide. 


If you have the option to be able to work on tracks and not the entire mix.... you can take something like the acoustic guitar (assuming it has one in it) and clone it, nudge it a bit, one way or the other, and pan it hard. It's better to record a second track but that is not always an option on the older tunes. 


By widening just one instrument that is in the entire song.... like the acoustic might be, you get the widening on that instrument without blurring the rest of the mix. The one instrument widened tricks the brain into hearing the entire mix as wider, and you still have good definition in the rest of the mix. 


The problem as I see it with the plugs that supposedly widen the mix is that they apply the widening to the entire song and the song looses it's character into the mess of widening.... sounds like reverb or chorus applied to the entire song. I don't think  I have ever heard a widening plug that I really liked when it was applied to the entire song. It is a whole different matter when it is applied to one or two selected tracks in a song. 


my 2 cents.

Sonitus phase will also do a mighty fine job of widening a mix.

Yep, check out the Increased Width preset in Channel Tools. Notice the parameters that are changed and adjust from there.

Scott

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Scott R. Garrigus - http://garrigus.com - SONAR X2 Power! - http://garrigus.com/?SonarX2Power
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iZotope Ozone 5 has a very nice widener that I use for the same purpose.....
You can select various bands and apply different widening (or none at all) for each band.

Channel tools ? I use it alot ....its great imo

Any kind of M/S-capable effect has the potential for enhancing width. Unfortunately, Channel Tools is the only bundled plugin that does. If you are open to third-party tools and have a few bucks to spend, look at FabFilter Pro-C and Pro-Q, both of which are very useful for widening. The perception of width comes down to left-right differences, so all width enhancing entails exaggerating or creating differences between the left and right channels. We are most perceptive to differences in the high frequencies (frequencies with wavelengths longer than the distance between our ears). The simplest trick is boosting high frequencies with an equalizer that allows separate processing of the Side component. Unlinking your limiter will also help, if your limiter offers that capability. Any compressor, limiter or EQ can be made into a M/S processor with a little work. Run a track to two busses, each with an instances of Channel Tools. Turn the Mid component all the way down on one bus and the Side component all the way down on the other bus. Now you have separate Mid and Side components that you can treat any way you like. Try putting reverb on the Side component only, for example.