Part 1 of this article is essential reading otherwise this part won't make as much sense as it should. All three parts consider mainly the steel-strung acoustic guitar.
There is a 'heroic' school of thought among guitar players that you should change your strings often, as often as every day, or even every song in a recording session. However, used (used, not old and worn out) guitar strings can often sound better than new strings fresh out of the packet.
New strings have a lot of 'zing', which can be very sparkly and attractive on single-note melodic lines, or open-textured finger picking. But when you start to add more notes to the harmonies, or play chords, then the zing from multiple strings adds up and becomes too much. Rapidly-repeated, loud, 6-note chords suffer particularly from this, and the sound can almost become choked. The notes, and the sound of the instrument, are clouded by too much zing.
In the world of guitar enthusiasts it is often said that when strings are new you hear the sound of the strings. When they have been played in and have become fairly well-used, you hear the sound of the guitar. There is a lot of truth in this, particularly when the instrument is recorded.
There is a point where strings have been sufficiently played in and they are in the 'golden zone' where they are still bright, but the zing is tamed to a reasonable extent. This golden zone can last for quite a lot of playing. When the strings start to sound dull to you as a player, they can still sound perfectly bright enough to the microphone. It also matters what the context of use of the guitar is. The acoustic guitar is often used as a 'thickener' in a track, like cornflour in a sauce, and doesn't need to be explicitly heard in its own right. Strings that are very well played in can be perfect for this application.
You could of course say, "If strings are too zingy, why not just EQ the zing out?". Well I would say just try it. You will quickly learn the limitations of EQ and why a good recording engineer will always try and get the best sound coming out through the cable of the microphone, by whatever means, rather than 'fix it' later.
It should be apparent from your existing experience with the guitar that strings change over time and usage. It is impossible to keep a set of strings in the same state. It is known for players, particularly those who record regularly, to keep and label up used strings so that they have a range of sets to choose from that are at different stages of use, and thus have different sound properties. This requires very good organizational skills, but if you're striving for the very best standards in all aspects of your playing and production, then it's worth considering.
In summary, when thicker textures are required, used strings have a freedom from the 'zinginess' that new strings have which leads to a choked and confused sound. However, the sound of used strings changes over time and that sound that a particular set creates has to be considered in the context of the recording being made.Come on the FREE COURSE TOUR