Editing Purr (section)

==Frequency, amplitude, and respiratory variation==
*Domestic cats purr at a [[frequency]] of 20 to 30 vibrations per second.<ref name="purina" />
*Eklund, Peters & Duthie, comparing purring in a cheetah (''Acinonyx jubatus'') and a domestic cat (''Felis catus'') found that the cheetah purred with an average frequency of 20.87&nbsp;Hz ([[egressive]] phases) and 18.32&nbsp;Hz ([[ingressive]] phases), while the much smaller domestic cat purred with an average frequency of 21.98&nbsp;Hz (egressive phases) and 23.24&nbsp;Hz (ingressive phases).<ref>Eklund, Robert, Gustav Peters & Elizabeth D. Duthie. 2010. [http://roberteklund.info/pdf/Eklund_Peters_Duthie_2010=Purring_Cheetah_DomesticCat.pdf An acoustic analysis of purring in the cheetah (Acinonyx jubatus) and in the domestic cat (Felis catus)] {{Webarchive|url=https://web.archive.org/web/20190214175643/http://roberteklund.info/pdf/Eklund_Peters_Duthie_2010=Purring_Cheetah_DomesticCat.pdf |date=14 February 2019 }}, ''Proceedings of Fonetik 2010'', 2–4 June 2010, Lund University, Lund, Sweden, pp.&nbsp;17–22.</ref> 
*Schötz & Eklund studied purring in four domestic cats and found that the fundamental frequency varied between 20.94 and 27.21&nbsp;Hz for egressive phases and between 23.0 and 26.09&nbsp;Hz for ingressive phases. Schötz & Eklund also observed considerable variation between the four cats as regards relative amplitude, duration and frequency between egressive and ingressive phases, but that this variation occurred within the same general range.<ref>Schötz, Susanne & Robert Eklund. 2011. [http://roberteklund.info/pdf/Schotz_Eklund_2011_Purring_DomesticCats.pdf A comparative acoustic analysis of purring in four cats] {{Webarchive|url=https://web.archive.org/web/20201116163504/http://roberteklund.info/pdf/Schotz_Eklund_2011_Purring_DomesticCats.pdf |date=16 November 2020 }}. ''Proceedings of Fonetik 2011'', 8–10 June 2011, Royal Institute of Technology, Stockholm, Sweden, pp.&nbsp;9–12.</ref>
*In a follow-up study of purring in four adult cheetahs, Eklund, Peters, Weise & Munro found that egressive phases were longer than ingressive phases in all four cheetahs. Likewise, ingressive phases had a lower frequency than egressive phases in all four cheetahs. Mean frequency were between 19.3&nbsp;Hz and 20.5&nbsp;Hz in ingressive phases, and between 21.9&nbsp;Hz and 23.4&nbsp;Hz in egressive phases. Moreover, the amplitude was louder in the egressive phases in four cheetahs.<ref>Eklund, Robert, Gustav Peters, Florian Weise & Stuart Munro. 2012. [http://roberteklund.info/pdf/Eklund_et_al_2012_Cheetah_Purring.pdf A comparative acoustic analysis of purring in four cheetahs] {{Webarchive|url=https://web.archive.org/web/20131102124748/http://roberteklund.info/pdf/Eklund_et_al_2012_Cheetah_Purring.pdf|date=2 November 2013}}, ''Proceedings of Fonetik 2012'', 30 May–1 June 2012, Gothenburg University, Gothenburg, Sweden, pp.&nbsp;41–44.</ref>
*Eklund & Peters compared purring in adult, subadult and juvenile cheetahs and reported that while there was considerable variation across most of the parameters analyzed (amplitude, phase duration, cycles per phase and fundamental frequency) – mainly attributable to degree of relaxation/agitation in the animals resting or playing– previously reported observations that ingressive phases tend to be lower in frequency were largely confirmed. There were no major differences in these parameters as a function of age.<ref>Eklund, Robert & Gustav Peters. 2013. [http://roberteklund.info/pdf/Eklund_Peters_2013_Cheetah_Purring.pdf A comparative acoustic analysis of purring in juvenile, subadult and adult cheetahs] {{Webarchive|url=https://web.archive.org/web/20200820212524/http://roberteklund.info/pdf/Eklund_Peters_2013_Cheetah_Purring.pdf |date=20 August 2020 }}. In: [http://roberteklund.info Robert Eklund] (ed.), ''Proceedings of Fonetik 2013, the XXVIth Swedish Phonetics Conference, Studies in Language and Culture'', no. 21, {{ISBN|978-91-7519-582-7}}, {{ISBN|978-91-7519-579-7}}, ISSN 1403-2570, pp.&nbsp;25–28.</ref>