This article describes the design and implementation of RASTA, a Real-time Audio Spectral Analysis Toolbox for Unity3D. Written in C#, RASTA provides an asynchronous, multi-threaded solution for extracting eight spectral and two time-domain audio descriptors in real time. Users have control over key parameters, including windowing type, FFT resolution, frequency bin exclusion threshold, and optional pre-filtering, enabling fine-tuned spectral analysis. Unlike Unity’s built-in spectral analysis methods, RASTA allows pre-filtering, adaptive frequency range selection, and customizable descriptor calculations, ensuring greater flexibility and efficiency. Designed for applications in interactive media, reactive visuals, musician-AI interaction, speech analysis, and machine learning, it seamlessly integrates into Unity’s C# ecosystem. By optimizing computational performance through multi-threading, RASTA enables low-latency spectral analysis without impacting frame rates, making it a powerful tool for developers working in game development, VR, digital art, and real-time sound-driven applications.