Editing Preferred number (section)

== Audio frequencies ==
ISO 266, Acoustics—Preferred frequencies, defines two different series of audio frequencies for use in acoustical measurements. Both series are referred to the standard reference frequency of 1000&nbsp;Hz, and use the R10 [[Renard series]] from ISO 3, with one using powers of 10, and the other related to the definition of the octave as the frequency ratio 1:2.<ref>{{Cite web|url=http://webshop.ds.dk/Files/Files/Products/18315_attachPV.pdf|title=ISO 266: Acoustics—Preferred frequencies}}</ref>

For example, a set of nominal center frequencies for use in audio tests and audio test equipment is:
{| class="wikitable"
|+Frequencies to be used in one-third octave analyzers in the audible range<ref>{{Cite book|title=Software-Based Acoustical Measurements|last=Miyara|first=Federico|publisher=Springer Nature|year=2017|isbn=978-3-319-55870-7|pages=21}}</ref>
!Nominal Center Frequency (Hz)
|-
|20
|-
|25
|-
|31.5
|-
|40
|-
|50
|-
|63
|-
|80
|-
|100
|-
|125
|-
|160
|-
|200
|-
|250
|-
|315
|-
|400
|-
|500
|-
|630
|-
|800
|-
|1000
|-
|1250
|-
|1600
|-
|2000
|-
|2500
|-
|3150
|-
|4000
|-
|5000
|-
|6300
|-
|8000
|-
|10000
|-
|12500
|-
|16000
|-
|20000
|}