Acoustic phonetics is a subfield of phonetics, which deals with acoustic aspects of speech sounds. Acoustic phonetics investigates features of waveforms as they pertain to the time domain (e.g. duration, amplitude, fundamental frequency), frequency domain (e.g. frequency spectrum), or combined spectrotemporal domains. Acoustic phonetics is also concerned with how these properties relate to other branches of phonetics (e.g. articulatory or auditory phonetics), as well as abstract linguistic concepts such as phonemes, phrases, or utterances.