Is there any Java or C# library for signal analysis using the sound card of a PC? I'm not interested in music mixing, rather in general purpose signal analysis - take a look at SIGVIEW - I'm interested in a Java or C# library that can do that. Another example is the scEEG project, striving to build a sound card electroencephalograph, by analyzing brain-wave signal captured by the sound card.
You can access audio inputs in Java using the JavaSound API (classes in javax.sound.sampled). The last time I used .NET for this, you had to use the managed DirectX API, which was not so easy to use, but newer .NET frameworks may have an easier API for this.
When it comes to signal processing, I guess you have to be a little bit more accurate about your requirements. It's a very broad field and it may or may not be available libraries to perform the analysis or processing you need, but no one can guess what you're up to.