Pacific Northwest DMR

Audio Test TG - VU multi-segment Meter and Level Testing

Most us of do not have a $42,000 AeroFlex 3920 DMR optioned Radio Test Set sitting on the kitchen table.  So here's a cheaper method you can try.  Very helpful if you have a spare radio and can dedicate a VU-Meter to monitor your favorite repeater.

A few members of PNW DMR do have this VU Meter, just ask for a test on by calling on WA 1 or 2, ask for a test, then move to Audio Test 2 to give it a go.

YOUR TARGET:  any yellows with 1 red or all green on average

20 Segment Barograph

50 Segment Barograph

TO TEST:  Always use your normal voice, normal position, under normal conditions.  Sounds easy but it is not. Ask if a meter reader is listening on Audio Test to help.

We suggest saying something like, "This is K6HOT, VU Audio Test 1, 2, 3, 4, 5".  To "exercise" your audio, you might say "4" several times; long and sustained.

This approach provides a better view of the bars and tends to be the hottest audio in the number string, as well as providing some averaging rather than instantaneous changes.

After a test sequence a VU meter owner will comments on what he sees.  You may listen also to the stream (~ 1 minutes delay)

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The 20 segment LED VU bar meter shown on the left provides an objective view of the range of talkgroup audio levels.  The target range is the 6 yellow bars  but 1 red square is acceptable on peaks.  The 50 segment works the same way but with better annunciation via the additional 30 segments.

The meter is adjusted so that reasonable audio (no piercing audio, no distortion and breath puffs minimized) is likely when your average audio falls within the yellow range.  This set-up provides a more complete "picture" of all audio conditions.  The actual dB values is less important in this context.  The peak audio level is held for 1 second and then falls away.

0dB = 3 reds (HOT HOT) // -3dB = 1 red (HOT) // -8 dB = 3 yellows (Perfect) // -12dB = 0-1 Yellow // -15db = 3 greens

The responsive range of this meter is 4-20 though the audio level input is can be lower than 4 and higher than 20. 

The VU meter is calibrated to a baseline of all yellow and green bars plus one red just flashing on the edge of illuminating while pressing Touchtone number 5 on a MotoTRBO XPR-6500 HT keypad as it sends out roughly 1,000hz (dual) tone.  The D878UV may also be used as the TT levels are fixed (set to LED 48 to just flicker on while pressing TT #5).  Calibration provides the dB levels vs LED segments as measured by my Sinadder 3 (More Info).

To test with this resource, always use your normal voice, normal position, under normal conditions.  Sounds easy but it is not.  Think about how other people use cell phones, they talk louder when unaware of the distraction they are causing.  Most people will speak softer when they are aware of the noise they are creating or in this case when the OTA level may be offensive.  Most users will again, speak softer when advised of their hot audio but it will creep back up when they forget about it later.  So try to resist that temporary reaction.  You could have your friends monitor your audio at random times and report back to you later as to where your audio falls when you are not thinking about your audio levels.  Most users tend to be offended, even if they don't indicate it.  So try to be gentle and diplomatic.  But a temporary solution by saying that you will talk softer or further from the mic IS NOT THE ANSWER.  You must reprogram for your voice and style or you will fall back into that old method of speaking to your radio and continue to violate acceptable levels of audio as well as the clarity of your speech.  This human tendency cannot be emphasized enough!  The radio must be adjusted and likely the user will need to modify the way they position the radio.  This is has been amazingly difficult to get users to do.  They don't need to listen to their own audio but we do!


Now using a 50 segment version to light the night <Ebay>

BUILD IT:  Most us of do not have a digital test test, so some other method that provides a way for us to quantify our (average) levels at a cost that a typical ham is able to afford is needed.  This approach outlined below costs $25 -$50 and works well for the end goal of having effective and pleasant audio.  A spare radio HT dedicated to the project is a huge plus.

Parts needed:

  • Radio that provided earphone level audio output or speaker output massaged to reduce the levels so you have mid-range volume pot to be approximate level to drive into the yellow LED's.

    • Interface connector/cabling from radio to your LED module (some connectors are hard to find)

    • May need a 50-100 ohm resister to enable the external speaker/earphone output

      • for the GD-77, I'm using the speaker/mic earphone jack with 120 ohms across tip and ring to turn on the external speaker function.

      • For the CS-580, I used a 10k/10k audio transformer via the speaker/mic

      • More details or a diagram later if there is interest

  • 30 segment 3 color LED VU module (30 segment green/yellow/red for Amazon, ~$40)

  • 20 segment 3 color LED VU meter (32 segment green/red sample from:  Ebay, ~$25) [NOTE:I am having issues with this Ebay 32 segment, FYI at this time only]

  • Once the audio level on the HT's volume control is set, mark it and then leave it alone.

    • You can leave the 580 in the charger 7/24 or use a battery eliminator pack.

    • Put the radio in digital monitor mode, single or dual slot so that you can "see" all traffic.

 


We hope that you will become "Audio Active" in that you will try to generate good audio over the PNW DMR network as well as help others to so.  If you hear poor audio, let the user know and over to assist them with your VU meter.  You don't need to be the "Audio Police" but you can make a difference if you make the effort on behalf of all members of our network.

 

 

 Revised: 01/29/2019 13:40

 

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