Periodic sounds give line spectra while aperiodic sounds give continuous spectra

Evidence

By way of contrast and to complete the story, sounds that have no definite musical pitch (but a pitch nevertheless—see what follows) associated with them, such as the “ss” in sea (Figure 3.9 later in the chapter), have an acoustic pressure waveform that does not repeat regularly, and is often random in its variation with time and is therefore not periodic. Such a waveform is referred to as being “aperiodic” (see Chapter 1). The spectrum of such sounds contains frequency components that are not related as integer multiples of some frequency, and there are no harmonic components. The spectrum will often contain all frequencies, in which case it is known as a “continuous” spectrum. An example of an acoustic pressure waveform and spectrum for a nonperiodic sound is illustrated in Figure 3.6 for a snare drum being brushed. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 822

Thus the main difference between the spectrum of periodic and aperi­ odic waveforms is that periodic waveforms have discrete partials, which can be represented as lines in the spectrum with a spacing that is inversely pro­ portional to the period of the waveform. Aperiodic waveforms by contrast will have a spectrum which is continuous and therefore does not have any discrete components. However, the envelope of the component amplitudes as a function of frequency will be the same for both periodic and aperiodic 7F Hz 5F Hz 3. — David Howard, Jamie Angus, coustics and Psychoacoustics, 456

Categorization

• DEFINE: Clear operational definitions of aperiodic waveform and continuous spectrum, with the snare drum brush and ‘ss’ as concrete anchors.
• QUESTION: The parenthetical ‘but a pitch nevertheless’ hints pitched/noise perception exists for these sounds too — worth chasing in Chapter 5.
• corroborated: 3 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 822; David Howard, Jamie Angus, coustics and Psychoacoustics, 456
• XREF: connects to: An amplitude-modulated tone produces a three-line spectrum; Two vibrations with an irrational frequency ratio never exactly repeat their combined pattern; Signals with autocorrelations that decay to zero need continuous spectra (+5 more)

Broader Connections

• Periodic and aperiodic spectra differ in discrete versus continuous partials #expands (0.95) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 460
• Periodic pressure waves are perceived as pitched while nonperiodic ones are not #corroborates (0.85) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 826
• Clear musical pitch arises from regularly repeating acoustic waveforms #corroborates (0.80)
• Clear pitch perception depends on periodic repetition of the pressure wave #corroborates (0.80) — David Howard, Jamie Angus, coustics and Psychoacoustics, 774