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This report explores broadband seismic signal processing aimed at extracting information relevant to several key aspects of nuclear monitoring, yield estimation, source studies and discrimination. The term 'broadband processing' in our definition refers to techniques designed for extracting the maximum information allowed by the S/N ratio from the data, using an information-theoretical definition, not the conventional waveform inversion of the so-called broadband seismograms, and estimating error bounds for parameters estimated. Another recurrent central idea examined and exploited in this report is the frequency-domain decomposition of multi-event, multi-sensor data into source and site factors. Various ensemble-averaged coherence measures can then be used to test the effectiveness of such factorization. In Section 1.0, we examine the spectral factorability of P sub n and Lg phases recorded at NORESS and the 3C subarray of NORSAR. Section 2.0 re-examines some aspects of estimating secondary arrivals (pP, spall, etc.) in teleseismic P waves and applying corrections to Mb. Section 3.0 explores ways to perform spatio-temporal source inversion using waveform data. In the last part of the report we describe an approach for S/N ratio enhancement, using the application of site waveform- equalization, together with adaptive filtering.