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audio-video systems design

The Phone Plug—Uses and Misuses

The ubiquitous phone plug, especially in the 1/4 inch (6.3 mm) size, is extremely confusing to the uninitiated. I was at a church today where I struggled to get a video to play properly in advance of an event in a few days.

The church had a PC and two 60-inch diagonal video monitors (another story). The audio was fed to the good-quality 16-input mixer (Allen and Heath, I think) from the PC’s headphone output.

In the video, there are two places where there is speech and the music is faded into the background. When played in the church, the voice disappeared! This created some angst coupled with erroneous assumptions. I hope this post will perhaps help solve this problem for others.

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The Digital Cliff and HDMI

I was at a church today where I struggled to get a video to play properly in advance of an event in a few days. There were issues with the application of a TRS phone plug (another story).

The church had a PC and two 60-inch diagonal video monitors plus a smaller monitor for the choir. There appeared to be a powered splitter/amplifier at the balcony console to split the HDMI to the two big monitors, with one cable running down each side of the church. I believe there must have been a second two-way splitter (hopefully another powered splitter/amplifier) to tap off the feed from the right main monitor for the choir monitor.

When I arrived, the PC was set up for 1024 x 768 display with the HDMI output mirroring the laptop built-in display. The laptop built-in display was capable of 1366 x 768. The slide show was a 16:9 WMV file. I tried expanding the display to the widescreen resolution and it was fine on the PC, but the monitors would not sync.

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Voltage and power matched audio in 2014

I received an email requesting clarification on my 1980 AES Preprint about the use of voltage audio distribution vs. power matched audio distribution for analog audio signals.

The confusion seemed to be about equipment being rated for driving a 600 ohm load. Yes, most professional audio equipment will drive a 600 ohm load, but might (repeat might) lose a small amount of headroom doing so. The better reason to be able to drive a 600 ohm load is to drive long cables which might create slew-rate limiting if they load the output to the extent that they slow it down. It’s all about current. In fact, merely being able to drive a 600 ohm load may not provide enough current to drive very long cables.

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