Using a Mackie 402VLZ4 and a 30 dB pad

[gcollett]

I am setting up a chapel for broadcasting using the suggested Teradek Vidiu (which the stake already had) with a simple JVC video camera with HDMI out (which is mine but little used and I am loaning it to the ward for now) on a tripod (which the stake already had) at the back of the chapel. The video works great. My first attempt for sound was to run a cable from the line level sound output jack at the pulpit directly into the Vidiu. After turning the Vidiu sound level up to maximum and turning the receiving computer's volume up to maximum, the sound level was barely acceptable.

I have gone ahead and purchased a Mackie 402VLZ4 mixer as suggested here: https://www.churchofjesuschrist.org/hel ... g=eng&_r=1 from a local audio equipment store in order to boost the signal strength. The instructions in the above link sat to put a 30 dB pad in-line on the output from the mixer. I had printed out the webpage of setup instructions and had information on the Vidui's specs with me. The gentleman helping me reviewed these and stated there was absolutely no need for the pad because the mixer took care of everything the pad would do and it would just drop my audio signal too low.

Why do the setup instructions say to use the 30 dB pad? What is its function? Do I really need one? Could not having one damage the Vidiu? Why would the store expert insist it should not be used?

[russellhltn]

Going by memory, the Teradek is "consumer level" line in. It should be a good match for the chapel audio out, unless the level has been turned down. You might check the facepate. As far as I know all of them have been line level outputs but you can buy a module that's "mic level".

The Mackie may be a "professional level" out. That's a bit hot for "consumer" devices and may cause distortion. However, 30 dB seem rather excessive.

I don't remember of the Teradek can be switch to mic level. But I think it's looking for a stereo signal, so you'd need to consider that. That might be one of the issues with existing connection.

[russellhltn]

Just remembered something. Inexpensive devices may use a "impedance matched" output that puts all of the signal on one side of a "balanced" output and none on the other. Depending on how you're going from a balanced output to the Teradek, that's going to leave you with either nothing or a very strong signal.

I'll try and do a deep-dive in the numbers tonight.

It's possible the selection of 30dB pad is because a pad was necessary and that value was easy to find.

[russellhltn]

Quick glance at the manual for the Mackie 402VLZ4 - the simple answer is to use the RCA "Tape Out" jacks. It's rare for RCA jacks to be anything but "consumer line level". A cable that goes from 3.5mm stereo TRS to a pair of RCA plugs is pretty common and cheap. Use that to go direct from the Mackie to the VidiU 3.5mm jack and you should be golden.

And yes, the Mackie is "impedance matched" and does produce "professional line level" at the 1/4" jack output. Trying to use that isn't worth it given the short cut of just using the RCA jacks. Less stuff, cheaper cables. The outputs are derived from the same source internally, so no change in operation.

I can do a deep-dive into the voltage levels and stuff if there's interest, but I think this answers the question.