We propose an approach to insert physical objects in audio digital signal processing chains, filtering the sound with the acoustic impulse response of any solid measured in real-time. We model physical objects as a linear time-invariant system, which is used as an audio filter. By interacting with the object or with the measuring hardware we can dynamically modify the characteristics of the filter. The impulse response is obtained correlating a noise signal injected in the object through an acoustic actuator with the signal received from an acoustic sensor placed on the object. We also present an efficient multichannel implementation of the system, which enables further creative applications beyond audio filtering, including tangible signal patching and sound spatialization.