which the sample is secured means for effectuating such rotation and controlling same are well known in the art the rotation rate of the rotor is observed with the spinning tachometer 32 a representative arrangement for providing such a signal is shown in fig2 and utilizes a reflective spot 40 on the periphery of the rotor 38 which is illuminated by light source 42 and observed by a photo diode 44 to provide a simple square wave signal 46 with a repetition rate representative of the rotation rate the timing pulse combined in gate 48 with a modulator select signal actuates a gate whereby the desired modulation is impressed on the respective rf carrier a first embodiment of the invention is further described in fig3 in a general sense rotor pulses are developed as above described and are applied to gate 34 i 34 modulator 14 for manipulation of the magnetization of a first nuclear species such as h 1 by a desired angle with respect to the magnetic field 21 immediately thereafter a long cross polarization pulse 34 cp 34 is applied to spin lock the 34 i 34 magnetization and cause precession of same about y in the rotating frame of i a similar spin lock and precession about.