Comments to date on reaffirmation of AES6-1982 (r1997), AES Standard Method for Measurement of Weighted Peak Flutter of Sound Recording and Reproducing Equipment published 2002-12-10 for comment.
Secretariat note: the comment period has been completed without unresolved comment.
Section 6.3 of this standard states that "The input impedance should not be less than 300 kilohms [sic] at 3150 Hz."
The 300 kOhm input impedance requirement is not met by many contemporary audio analyzers including those from industry leaders Audio Precision, Rohde & Schwarz, Tektronix, Agilent (aka Hewlitt Packard), Neutrik, etc. The measurement of wow and flutter does not require accurate knowledge of absolute signal level. Indeed, there is hopefully little correlation between signal amplitude and wow and flutter except at such low levels where noise begins to affect the measurement.
The real issue is that the loading effects of the analyzer input shall not disturb the wow and flutter sideband relationships. In other words, the analyzer input impedance should cause only a frequency independent gain error about the 3.15 kHz (or 3.00 kHz) test frequency. Assuming the output impedance of the device being measured is reasonably linear and resistive, this condition is met with almost any resistive input impedance.
To avoid the technical disqualification of many good audio analyzers I implore you to consider changing the text of section 6.2 to: "The input impedance should not be less than 100 kOhms at 3150 Hz."
Bruce E. Hofer
Administratively, this was simply a call for comment on reaffirmation which was forced by our mandatory five-year review process. A revision is due in the reasonably near future, but if we don't reaffirm the present standard, we won't have anything to revise!
If it is acceptable to you, we'll handle this issue as part of the revision, as well as various other updates to bring it in line with current terminology and style.
Technically, I agree with your comment, and will recommend its inclusion in the revision. In the meanwhile, the instruments with 100 kilohm input impedance are not disqualified even under the present standard - all new AES standards contain this:
NOTE: In AES standards documents, sentences containing the word "shall" are requirements for compliance with the document. Sentences containing the verb "should" are strong suggestions (recommendations). Sentences giving permission use the verb "may". Sentences expressing a possibility use the verb "can".Actually, this has "always" been the implicit standards meaning of "should", but now it is explicit.