Below, you can see a range of signals, generated with MATLAB, whose signal-to-noise ratios (SNRs) span from -6 dB (which is equal to the ratio of 0.5 in the voltage scale) to 33 dB (the ratio of 45 in the voltage scale), arranged from the lowest to the highest SNR value.

These signals' background noises have equal root mean square (RMS) values, whereas their signal values change. In order to make signal comparison as easy as possible, all the signals' charts have the same axes scales.

The only thing that needs to be taken into consideration here is the relation between the signal level and its respective noise level (see Figure below). What you choose here is the signal with the worst (that is, the smallest) difference between its magnitude and its background noise which you consider good enough to be presented as a satisfactory result of an NMR measurement.