The ASDEX Upgrade tokamak employs a 60-channel electron cyclotron emission (ECE) radiometer diagnostic for the measurement of radial electron temperature profiles of the plasma. The data acquisition (DAQ) portion of the system has now been upgraded to sample at 1 to 2 MHz, and accordingly, electron temperature fluctuations from 500 kHz to 1 MHz may be measured. The high spatial resolution of [approximately]1 cm and flexible magnetic field coverage from 1.5 to 3.0 T remain unchanged. The system can now provide observations of plasma phenomena on the magnetohydrodynamic timescale, such as neoclassical tearing modes (NTMs) and toroidal Alfvén eigenmodes (TAEs). The upgraded and existing DAQ systems may be run in parallel for comparison, and some of the first plasma measurements using the two systems together are presented, along with an example of localization of [approximately]120-kHz TAEs in the fast ECE data. A principal planned application of the upgraded radiometer is integration into a real-time NTM stabilization loop using targeted deposition of electron cyclotron resonance heating (ECRH) or electron cyclotron current drive. For this loop, it is necessary to determine the locations of the NTM and ECRH deposition using ECE measurements. The NTM location is determined via correlation between ECE and Mirnov coil measurements, and results of this technique for (2,1) and (3,2) NTMs are presented. ECRH deposition is located by observing the modulation signature of the injected ECRH power in ECE measurements. Several additional applications enabled by the upgraded radiometer are also discussed.