Editing Audio system measurements (section)

==Automated sequence testing==
Sequence testing uses a specific sequence of test signals, for frequency response, noise, distortion etc., generated and measured automatically to carry out a complete quality check on a piece of equipment or signal path. A single 32-second sequence was standardized by the [[EBU]] in 1985, incorporating 13 tones (40&nbsp;Hz–15&nbsp;kHz at −12&nbsp;dB) for frequency response measurement, two tones for distortion (1024&nbsp;Hz/60&nbsp;Hz at +9&nbsp;dB) plus crosstalk and compander tests. This sequence, which began with a 110-[[baud]] [[Frequency-shift keying|FSK]] signal for synchronizing purposes, also became [[CCITT]] standard O.33 in 1985.<ref>{{cite web|last=ITU-T Recommendation|title=Specifications for Measuring Equipment – Automatic Equipment for Rapidly Measuring Stereophonic Pairs and Monophonic Sound-Programme Circuits, Links and Connections|url=http://www.itu.int/rec/T-REC-O.33-199507-I/en}}</ref>

[[Lindos Electronics]] expanded the concept, retaining the FSK concept, and inventing segmented sequence testing, which separated each test into a 'segment' starting with an identifying character transmitted as 110-baud FSK so that these could be regarded as 'building blocks' for a complete test suited to a particular situation. Regardless of the mix chosen, the FSK provides both identification and synchronization for each segment, so that sequence tests sent over networks and even satellite links are automatically responded to by measuring equipment. Thus TUND represents a sequence made up of four segments which test the [[alignment level]], [[frequency response]], [[noise measurement|noise]] and [[distortion measurement|distortion]] in less than a minute, with many other tests, such as [[Wow and flutter measurement|Wow and flutter]], [[Headroom (audio signal processing)|Headroom]], and [[Crosstalk measurement|Crosstalk]] also available in segments as well as a whole.{{Citation needed|date=November 2007}}

The Lindos sequence test system is now a 'de facto' standard {{Citation needed|date=November 2007}}in broadcasting and many other areas of audio testing, with over 25 different segments recognized by Lindos test sets, and the EBU standard is no longer used.