Bit late on this reply, but contains info some others might find useful...
There are 2 copyrights you need to be aware of for this kind of thing.
1) The musical copyright (that's the actual tune/song/melody etc itself)
2) The copyrights associated with the printed music (the Typographical Representation of said work)
Copyright lengths are different depending on your country (and several other lesser factors). In the UK, the musical copyright generally lasts for the life of the composer + 70 years. As long as the composer died more than 70 years ago, the musical copyright has expired - you can use the tune for whatever purpose you wish.
However, just because a tune is out of copyright doesn't mean you can go ahead and record it...
The "typographical representation" copyright lasts for 25 years and it's this are that is very misunderstood.
The typographical representation is the printed layout of the music. You may not perform in public, record or in any way reproduce the music from a typographical representation of a piece of music when that typographical representation is under copyright.
For example, a piece by Mozart is obviously out of copyright, but a publisher who publishes an edition in 2004 has copyright over their edition (you may not record, perform in public, photocopy etc). Even though the music (as in melody) is out of copyright, you would be using a copyrighted edition as the basis for your activities which (unless you have paid for a licence or have their express permission is illegal).
This is why you can't just use a score published last year and re-write it in your on hand - the origin of your work is still under copyright and your work would then be derived from something that somebody else holds copyright for. In order to do your own versions, you must
work from an edition that is no longer under copyright.
Now, publishers often re-publish but when they do they do NOT regain copyright. If the edition is identical and just a re-print, the copyright runs from the first
publication date. Having said that, it would be your responsibility to prove the first date of publication of that edition.
Even when a publisher changes certain things, what many people don't realise is that they don't gain copyright over the whole layout again, they only gain copyright on the additions and changes. If the notes are the same, then you may copy them for your own purposes and add your own bowing, articulations etc.
An arranged piece of music is classed as a derivative work for which the arranger (not composer) gains the lifetime+70years copyright.
The problems occur when a piece is edited. To be classed as a derivative work, it must be substantially different from the original. Exactly how much editing makes a published edition a derivative work is a very grey area and one that would only be decided on a case by case basis and probably in a court of law. If an edited (rather than arranged) edition is thought to be under copyright as a derivative work, then the copyright lasts for the lifetime+70 years of the last surviving member
of the editing team!!
Having said all that, most publishers and composers I've dealt with will grant permission to perform. To record and sell a CD is a different matter and would require you to buy a licence to do so. Most countries have a Performing Rights body (in the UK, it's the PRS for live performance and MCPS for recording, broadcasting and synchronisation) which will give you the information on which type of licence you'll need and how much it will be.
They represent the copyright holders and act as the go-between.
Cheapest option - find out of copyright music with out of copyright published editions and use those, or do your own arrangements from them.
Easiest option - get a list of the pieces you want to record along with the composers and publishers names and contact the relevant mechanical copyright body in your country.
*N.B all copyright lengths and info based on discussions with and info from the UK Patent Office and the UK Copyright Service