Comments to date on DRAFT REVISED AES17-xxxx AES standard method for digital audio engineering — Measurement of digital audio equipment
published 2015-07-20 for comment.
The comment period has closed.
I would like to comment on Annex C of aes17-xxxx-150720-cfc.docx. page 39/39. There is the Informative reference mentioned:
* Harris, F. J. On the use of windows...
Here it would be practical to mention also the following, later reference:
* Nuttall, Albert H. Some Windows with Very Good Sidelobe Behavior, IEEE Transactions on Acoustics, Speech, And Signal Processing, Vol. ASSP-29, No. 1, February 1981.
The author comments directly on Harris' paper, corrects, and extends it. The Abstract reads: "Some of the windows presented by Harris  are not correct in terms of their reported peak sidelobes and optimal behavior. We present corrected plots of Harris' windows and also derive additional windows with very good sidelobes and optimal behavior under several different constraints. The temporal weightings are characterized as a sum of weighted cosines over a finite duration. The plots enable the reader to select a window to suit his requirements, in terms of bias due to nearby sidelobes and bias due to distant sidelobes"
The paper by Nuttall is very handy for precision FFT measurements, and it can be considered as classic.
Regards, Hartmut Henkel
Dear Mr. Henkel,
Thank you for your comment on the draft AES17-xxxx, posted 2014-07-20 for comment.
I note that you are proposing an additional informative entry in the informative annex C.
This can be done as an editorial matter, and a decision to do so can be made by the Working Group chair without impeding the progress of this draft standard.
Mark Yonge, AES Standards Manager
One of our best guys on this topic internally said the following after I circulated to document to internal experts:
Paragraph 6.6.2 [states]
"Next, the clock test signal shall have its phase jittered with a sinusoidal jitter signal. The frequency of this jitter test signal shall be varied from 80 Hz to 20 kHz in steps of not more than one octave. The jitter level shall be equal to the high frequency jitter tolerance limit of the interface used. If this level is not known, a value of 40 ns shall be used.”
I think that a "jitter level” of "40 ns” is ambiguous. Is 40 ns an rms or a peak-to-peak quantity? Is it integrated phase noise, time interval error, absolute time jitter, single-period jitter, N-period jitter, cycle-to-cycle jitter, or something else? Was the jitter spectrum band-pass filtered? This should be stated more explicitly, perhaps following the recommendations of AES-12id-2006.
Tomlinson Holman, Apple Inc.
Dear Mr. Holman:
Thank you for bringing up the matter of further definition for the 40 ns jitter signal. The document could, indeed, benefit by having a more explicit definition. To that end, the paragraph referenced in 6.6.2 shall be modified to read:
“Next, the clock test signal shall have its phase jittered with a sinusoidal jitter signal. The frequency of this jitter test signal shall be varied from 80 Hz to 20 kHz in steps of not more than one octave. The jitter level shall be equal to the high frequency jitter tolerance limit of the interface used. If this level is not known, a peak levelvalue of 40 ns time interval error (TIE) jitter shall be used.”
Please note: the underlined words in red point out the changes in language adopted for the purpose of this communication only; the document will use plain text.
In particular, the last sentence referenced above shall read:
"If this level is not known, a peak level of 40 ns time interval error (TIE) jitter shall be used."
Please reply by the end of the comment period if this reply is not acceptable to you. You may ask us to consider your comments again for the next revision of the document. You may also appeal our decision to the Standards Secretariat.
Vice chair, AESSC subcommittee SC-02 on Digital Audio