normalized to become amplitude proportion envelopes, where at each time frame all the harmonic amplitudes will add to 100% (or 1). This way, the main loudness-controlling envelope can be cleanly controlled. In Sound Recognition, max amplitude normalization can be used to help align the key harmonic features of 2 alike sounds, allowing similar timbres to be recognized independent of loudness. See also Complex amplitude Waves and their properties: Envelope Frequency Wavelength Crest factor Amplitude modulation Body thermal amplitude Atmospheric thermal amplitude Wave height Notes Physical quantities Sound Wave mechanics