The first figure below shows simulations (carried out in TOPSPIN) for an isopropyl group as a function of the C-H chemical shift. One can see the typical septet -doublet pattern when the chemical shift difference between the methyl and CH protons is much greater than the coupling constant. When the shift difference is comparable to the coupling constant, complicated second order spectra are obtained. When the shift difference is zero one obtains a singlet.
The left panel of the second figure shows the isopropyl region of the experimental NMR spectrum of (triisopropylsilyl)acetylene. The complicated second order spectrum is simulated in the right hand panel.
Thank you to Mattieu Leclere for providing the sample used in the figure above.