High frequency fluctuations are observed in JET by edge magnetic probes and arrays of visible radiation detectors even in the absence of Mirnov activity (typical frequency: ~1kHz); cross-correlation techniques are applied in order to study the broadband activity. Magnetic fluctuations (bq) in the range of 1 to 20kHz are strongly correlated along a direction parallel to the edge magnetic field lines; above ~10kHz, a substantial fraction of these fluctuations (30-60%) have low wavenumbers (m ≤ 5, n ~ 1). Fluctuations in visible radiation coming from the edge are detected by soft X-ray diodes (without absorptive foil) up to ~100kHz: correlation analysis indicates the presence of rather high m numbers (m ~ 10-100) with a correlation time of τc ~ 20μs. This type of activity is also seen by the magnetic probes and a good correlation between the two diagnostics is observed. The edge magnetic root mean square level is continuously monitored with eight hardware filters over the 5 to 60 kHz frequency range. Database analysis of additionally heated discharges shows a proportionality between tilde bqN = bq . BT/Bq and the inverse energy confinement time, (τE-1).