Because of the vast number of existing consonants they are much less distinct acoustically than vowels. The way they are articulated, however, finds an acoustic representation, which can be made visible. An important aspect here is the distinction between stable and dynamic sounds. For example, stops are dynamic consonants, which cannot be significantly prolonged, whereas nasals or semivowels (approximants) are relatively stable and can therefore be prolonged. Impulse-like sounds usually have more energy in an acoustic representation, whereas continuous sounds simply show a longer signal. Generally, there is a close physical relationship between the manners of articulation or the places of articulation and the acoustic signal one gets. If we do a Fourier-analysis for a consonant (or vowel), we will see that lip-rounding, for example, lowers all frequencies.