All musicians, at all levels need reference resources.
Where can I get ... a new bass trumpet mouthpiece, reeds, good studies for technique development etc?
What music has been written for ... (name your passion)?
How can I listen to the best performances of ...?
Before the genius of Tim Berners-Lee, getting answers to such questions needed much more effort than is the case now.
The development of the internet has enabled, from almost anywhere in the world, immediate access to information covering most periods and aspects of music - from studying the old masters of centuries ago, to hearing the latest performances taking place in 'real time'. Once the classic studies, methods, compositions or other writings or performances are out of copyright, they quickly become freely available to all.
Many of the major symphony orchestras and jazz groups now have live concerts available for download or streaming.
Just one example of the riches available on the web is US NPR's (National Public Radio) archives. They contain masses of interesting audio, documentaries and transcripts on Classical, Jazz, Rock and other specific genres. Once at the site, choose 'GENRES' from the menu at the top of the page.
Much is available for FREE download from sites such as the huge IMSLP site. Nearly all the music available at IMSLP is of a classical nature, but can be a gold mine for musicians of any genre wanting to study orchestration methods and instrumental voicings as used by old and not so old masters like Ravel, Debussy, Tchaikovsky, Stravinsky etc. At that same site are also many of the classical instrumental 'tutor' books.
The Live Music Archive site has thousands of playable examples of (mainly American) concerts and recordings of many genres of music.
[ Instead of downloading each time to hear a particular piece, a better method is to use a web recording programme. Two of these ('TotalRecorder' and 'Web Stream Recorder') are listed under Electro and Software - Web recorders. The cheapest versions of these are for audio only, but that should be enough for musicians - real musicians don't need visual appeal? ]
To quote Artie Shaw (commenting on his musicians doing visual tricks such as holding up their instruments and swaying in unison) "I said the audience doesnt know its fun. They think you're doing showmanship. And if we have to do showmanship that means we're very insecure about the music. Sit down and respect what you do. If you dont, they won't. .For musicians, an advantage of keeping copies of pieces on your own storage is that (apart from avoiding the need to download each time,) exercises such as transcribing become so much easier as the piece can be loaded into a program like Audacity then replayed at a speed which is comfortable for your transcribing skills.]
It is now quite easy to let others hear your latest efforts by attaching clips to emails or uploading videos or sound files to YouListen, YouTube, Facebook etc. There is nothing as valuable to a performer as getting feedback from colleagues, but a good second-best is getting opinons from the 'real world'.
For many free books on music and almost anything else, the Gutenberg Project is the site.
For those of us who are curious about the nuts and bolts of why music 'sounds', the not-too-technical bible is von Helmholtz's "On the Sensations of Tone", a great work! The Dover publication is available quite cheaply (~$10 secondhand) from the larger web bookstores. Alternatively, the .pdf version is available as a free download from Archive.org [N.B. over 60MB !].
Another very practical resource is instrument fingering charts (most at the source "The Woodwind Fingering Guide"). As with all fingering guides, the fingerings for altissimo registers become very much dependent on each individual instrument's physical characteristics, so what works on one instrument may be almost unusable on another.
For the nuts and bolts of DIY music synthesis, visit Bernie Hutchins' ELECTRONOTES site. It contains masses of information on topics ranging from music synthesis theory to DIY PCBs for synths, much of it free to download.
Some of the links go to pages in languages other than English, but as most browsers now offer spontaneous translation, this should not be a problem. The links on this page also list instrument manufacturers, repair DIY, instrument techniques, practice methods, music-associated electronics, wind synths, retail outlets [which I use - so it is biased - make some suggestions!], on- or off-line ear training programmes, music notation or performance software, and anything that doesn't fit comfortably elsewhere !