Hello Andrea,
Good question. Are you wanting to create a user client section where they can upload files via the front end of your site?
To create the login and access control portion you can use a plugin like Restrict Content (https://wordpress.org/plugins/restrict-content/). That will give you the ability to set some content on the site for logged in users and some for everyone.
For the file uploading, there probably are several plugins you could use for that. I’m a Gravity Forms user myself and one of the field types is an file upload one. So I typically just create a form and add that field in it. But it’s not a free plugin.
I believe Visual Form Builder (https://wordpress.org/plugins/visual-form-builder/) has an upload field and it is free. I could be wrong about that, but I believe that’s the case.
What you could do is create a your form and then create a new page on your site for it. Use the Restrict Content plugin to make it only accessible to logged in users. Then once it’s published you’ll have a spot where clients can log in and add their audio files.
There’s more than one way to do that I’m sure, but that’s not a bad way to start.
Have a great weekend,
Bill