The meeting was convened at 10:30 by acting chairman B Olson.
Editorial Note: The group is still looking for a permanent chair. Most of the work is done via electronic means between the meetings at conventions and that people can participate or even chair bi-annual convention meetings remotely. If anyone is interested in chairing the group they do not need to be able to physically attend the convention meetings.
In attendance were P Treleaven, B Olson, A Kuzub, R Cabot, J Britto, J Schmidt, C Lastrucci.
The formal notice on patent policy was read.
The meeting agenda was accepted as written.
Minutes of previous meeting in Milan, 2018-05-25 were approved.
Projects assigned to this group but not mentioned here had no action requested or required - see www.aes.org/standards/meetings/project-status.cfm for details.
AES48-R: AES standard on interconnections - Grounding and EMC practices - Shields of connectors in audio equipment containing active circuitry
Scope: This standard specifies requirements for the connections of the designated shield contact of connectors built into audio equipment using active circuitry. These requirements are necessary for the preservation of electromagnetic compatibility (EMC) at both audio and radio frequencies.
Discussion: This standard had been stabilized. The process to bring it out of stabilization has been completed and revision of the document was assigned to this working group.
The chairman reviewed the issue with the current version, that the figures mislead people as to proper grounding technique when implementing digital audio systems. The figures imply that ground currents from EMI filters should be routed through a star ground arrangement. This is opposite to best practice for digital systems which normally shunt EMI current to the shielding enclosure at the point of entry. R Cabot reviewed the technical details, specific problems with each figure and the proposed revisions to the figures. He also reviewed some minor changes to the corresponding text. Considerable discussion ensued about the specific paths of shield currents and the practical implementation when building equipment. There was some concern whether people would correctly interpret the meaning of the words "shield", "ground", "equipment ground" and "safety ground" as used in the text. The chair reminded people that the existing text was a compromise over several years of discussion on the proper use of these terms. Additional discussion focused on the differences required between shielded and unshielded enclosures and proper ground connections in the two cases.
A Kuzub raised the issue of extending the drawings to multichannel connectors. There was much discussion of whether the drawings and text adequately cover these cases. The chair noted that the examples were designed to handle the general case of properly implementing a connector and were not intended to be limited to single channel connectors. As the discussion progressed it became clear that much of the concern was about the proper connections for the multiple shield pins of these connectors. This is within the scope of AES59 which unfortunately does not reference AES48.
Other minor changes required to make the style conform to current IEC requirements were reviewed by the Standards Manager.
The group also discussed including an additional example covering improper routing of EMI filter return current.
No activity to report.
No new business.
The next meeting will be scheduled in conjunction with the AES 146th Convention, to be held March 2019 in Dublin, Ireland.