  We present the architecture of the versatile NMR spectrometer with
software-defined radio (SDR) technology and its application to the dynamically
controlled pulsed magnetic fields. The pulse-field technology is the only
solution to access magnetic fields greater than 50 T, but the NMR experiment in
the pulsed magnetic field was difficult because of the continuously changing
field strength. The dynamically controlled field pulse allows us to perform NMR
experiment in a quasi-steady field condition by creating a constant magnetic
field for a short time around the peak of the field pulse. We confirmed the
reproducibility of the field pulses using the NMR spectroscopy as a high
precision magnetometer. With the highly reproducible field strength we
succeeded in measuring the nuclear spin-lattice relaxation rate $1/T_1$, which
had never been measured by the pulse-field NMR experiment without dynamic field
control. We also implement the NMR spectrum measurement with both the
frequency-sweep and field-sweep modes and discuss the appropriate choice of
these modes depending on the magnetic properties of sample to be measured. This
development, with further improvement at a long-duration field pulse, will
innovate the microscopic measurement in extremely high magnetic fields.
