In the process of putting together Anglo, English and now Duet(Concertina) Internationals I have listened to hours upon hours of archive cassette recordings and sadly a very small percentage is usable.It is extremely frustrating listening to some remarkable playing with someone suddenly opening and closing a squeaky door,large objects being dropped to the floor,a dog barking,a child crying,a coughing fit and talking,which is just part of the frustration.Even without one of these noises the artist can make a mistake.With modern equipment this can be sorted out, the mistake erased and a passage, where he or she does get it right, can be inserted in.Some remarkable work was done to get Andrew Blakeny Edwards tracks suitable for the Anglo Collection, the original was nothing like the final recording used.
Continuous background noise can also be taken out such as humming ,crackling or even tape disintegration by modern computer methods.Likewise 78 recordings by using different methods like special needles or computer cleaning,can almost bring these recordings back to their original state.One of the most important things to remember is that the noise before the recording starts MUST be retained.This is used in the computer process and any hum crackle etc can be programmed into the computer from that section to remove that noise.
Jim Ward Crawley Sussex is an expert at this sort of work and did a wonderful job with the old archive recordings.
The method I use which may help is that on each cassette I write down those recordings (either by track number or by tune name )which are possibilities.I assure you after a few hours of it the good recordings stand out.When all the tapes have been listened to.Just extract those ones which you liked and then listen to the best as a package.Once again certain tracks will outshine the others.In this way you finish up with a final line up and it is then that recording doctoring may be required.
I hope this info help a little bit for those of you contemplating this type of project.
Al