Comments on draft revised AES11

last updated 2003-10-24

Comments to date on DRAFT AES11-20xx, DRAFT REVISED AES recommended practice for digital audio engineering - Synchronization of digital audio equipment in studio operations. published 2003-07-10 for comment.

Comment from Chris Woolf, 2003-07-11

The standard limits itself to ...

(1.2.1) to studios or studio centres - by implication "bricks-and-mortar" structures
(1.2.2) studios with external inputs
(1.2.3) audio slaving to video in a self-contained area (which just might be read as not necessarily a bricks-and-mortar studio).

However the standard would appear to be just as applicable to the ever-increasing non-studio applications such as two digital audio recorders locked to each other to give multi-track facilities on location, wireless locked video and audio recorders in the field, and any number of other imaginable combinations.

The phrasing of several parts of 1.2 would need adjusting but the terminology of "self-contained grouping" would seem to cover all such assemblages of equipment, with "studio" and "studio environment" perhaps better used as illustrative rather than definitive terms.

Page 6 table 1 - perhaps it should be "PAL is phase-alternation line" instead of "PAL is phase-alteration line rate"?

Chris Woolf

Reply from Robin Caine, 2003-07-18

With regard to Chris Woolf's comments:

1) Scope:

The scope is I believe sufficient by way of the expression 'self-contained area' in 1.2.1 and 1.2.3. Larger areas are affected by propagation/transmission delays, and are not addressed by AES11.

Since this has never raised any comment in previous revisions, I would prefer to leave well alone.

2) References to PAL, NTSC and SECAM

The substantive detail is in the mathematically precise numerical values.

PAL, SECAM and NTSC are only referred to in 4.5 and 5.3.4. In each case it is an expansion, an aide memoire. The Note in the table in 4.5 is more than adequate, except that it says 'phase-alteration....' not 'phase-alternation....', the latter being correct.

Robin Caine
[Secretariat note: the expansion of the abbreviation, "PAL", will be corrected to read, "Phase Alternation Line".]

Response from Chris Woolf, 2003-07-20

I am content with that reply.
Chris Woolf

Comments from Stephen Scott, 2003-10-06

Re: sub-clause 4.5
a.) 24 Hz is now a commonly used rate for television. The column heading in table 1 should reflect this by changing "24-Hz motion picture" to simply "24-Hz"

b.) Also 24/1.001 Hz is commonly used as a frame rate for television. A column should be added to table 1 with a heading "24/1.001-Hz TV" and entries of "4004/3", "2002", and "147147/80" for 32, 48, and 44.1 kHz respectively.

Re: sub-clause 5.3.4
For NTSC video the video frame reference point (vertical sync) is line 4 frame 1. For all other 59.94 or 29.97 Hz related television systems vertical sync begins at the beginning of line number 1.

In this clause, the related figure 1 and also figure A.1 in Annex A; revise the text "line 1" to "line1 (line 4 for the 525/59.94 video system)" or "line1 (line 4 for NTSC)".

Also related to this, the video standards are needed for implementation. SMPTE 318M should be moved from the bibliography to the Normative references clause. SMPTE 318M in turn references SMPTE 170M (525/59.94 video) and ITU-R BT.470 all conventional video standards.

Reply from Robin Caine, 2003-10-24

Re: sub-clause 4.5

a) Agreed, the words 'motion picture' will be removed from the column heading

b) This video standard was considered along with a number of nascent computer video standards but, due to their proliferation and uncertainty as to which would become common-place, the table was limited to those known to be in common use. The table is in no sense exclusive. This case will be included in the next revision.

Re: Sub-clause 5.3.4

We note that the wording in 5.3.4 refers only to the case of integer AES3 frames per video frame; this excludes the 525/59.94 system by definition.

To distinguish the case of 525/59.94 more clearly, a note will be added to both figures 1 and A1 to say 'Note: For 525/59.94 video systems the timing reference point would be line 4'

We propose to add an informative reference in Annex C to SMPTE RP168 to illuminate the 525/59.94 case.

I trust this will be acceptable.

Regards, Robin Caine, Chair SC-02-05

AES - Audio Engineering Society