It is a fundamental, underlying principle of all spectroscopy that the more absorbing species that exist in a molecule, the greater the observed signal. The standard proton is almost 100% abundant, whereas the spin active carbon nucleus is approx. 1% abundant (the remaining 99% are non-spin active isotopes). To a first approximation proton NMR spectroscopy should be much more sensitive than carbon NMR spectroscopy, and indeed it is. A proton NMR spectrum can be acquired in about 5 minutes with good signal to noise; carbon NMR spectra typically take a couple of hours (or overnight) and the signal to noise is much poorer. The proton nucleus is intrinsically much more sensitive than this in NMR experiments.