Home    PNW TRBO    News    Netwatch    Dash    Repeaters    Talkgroups    c-Bridge    Linking    Open IPSC    MTUSA

Site Map

Audio Levels and AGC Information

AGC UPDATE:  Gen 1 MotoTRBO radios running R01.12.02 firmware can now run with Digital AGC enabled as the radio now handles audio much better than the past 4 years firmware versions.

Not so New:  Generation 2 radios seem to have better implementation of AGC.  At this point, everything below applies to generation 1 subscriber radios.  But please be aware how critical correct audio levels must be on the networks.

Now Available: LED VU Meter on the LiveStream Video for objective testing

TRBO audio can be "Ear Piercing Loud" on first syllables and breath puffs across the mic, which causes listeners to dive for the volume control.  The wide levels of audio coming across the repeaters and networks makes it difficult to hear the soft users as hot audio causes users to turn down their volume.  Conversely listening to soft users will position other users to get blasted at random times.  Routine or background monitoring of the various TRBO networks is made more difficult and this page is an effort to identify some middle ground...if that is even possible.

Much of the rest of this page is now stale (legacy) but is left intact to show how huge a problem audio has been in ham TRBO for years.  Your efforts are appreciated to maintain pleasant audio and levels.

MotoTRBO radios can be programmed to enable AGC action on the mic inputs and this setting is enabled by default.  Some issues have surfaced that have caused us to re-visit the default use of AGC in the digital mode.  At this point, it is our recommendation or suggestion, at least starting out the gate, to use AGC if and only if you do not wish to test your radio and your voice characteristics.  This is easy to test using the VU Meter.  The following settings based Motorola and owns testing.  Your own experimentation is preferred method to get your unique audio levels dialed in. 

To further add to this sticky wicket, R01.08.10 mobile radios now have a new "noise suppressor" function which may reduce audio by about 2 dB in some cases. 

Suggested settings PDF by Mike, AA9VI, 4-24-2013

Suggested Settings from a Motorola  (click for larger Image)

Thanks to Steve, KF0RW for supplying the above image

Legacy Testing which may or may not be the best approach with the latest firmware

All in all, this effort is going to be a monster to get correct with all the different types of radios, microphones, voices and mic holding styles.  So, our bottom line, just please be aware of your audio, ask for reports and compare other audio levels and let folks know when they are very hot or soft relative to the other audios in a given conversation.  Some thought now given to returning to AGC enabled and simply try to get people to back away from their mics, though this is likely just going to perpetuate the audio blasts that began this testing episode. 


AGC is disabled and Noise Suppression enabled!

+5 dB

HT's: all around use; 2" @ 45 degrees typical
+7 dB HT, with speaker mic exclusively;  2" @ 45 degrees typical
+4 dB Mobiles with standard mics;  2" @ 45 degrees typical
+2 dB Mobiles with Impress Touch Tone mics; 2" @ 45 degrees typical
0 dB Mobiles with Impress Base mics; 12" from mic, typical tabletop use when seated, not closer than 2", rear level pot about mid-range
Lower overall gain setting if you tend to close talk, have a loud voice or are in a noisy environment.  If using 8.10 firmware in mobiles, please see the notes.

With so many repeaters and networks now linked together, there is more range in audio levels now being heard.  One of the primary issues in audio levels is the AGC's tendency to produce super hot (PIERCING) audio levels briefly at the beginning of a voice encoding.  It is quite obnoxious and makes it difficult to monitor the traffic on the network, especially when listeners are in a mixed-mode environment of family, work or TV viewing, etc.  Less of an issue but still valid, is simply the wide range of user voices differences and how the mic is positioned relative to the mouth.  Also significant though short term or random, are issues such as breath puffs across the face of the mic, wind and ambient noise.

While AGC works well most of the time for most people, those lesser times are bad enough to force us to look at options.  Hence, the recommendations above and our less than scientific method testing results below.  If you have any input, we always appreciate the comments, corrections and/or suggestions: Email us

Some users have stated they use settings as low as -5 dB.  Our settings above are the HIGHEST recommended.  Feel free to lower your settings if that fits your normal uses better.  TRBO radios have very high speaker volume capabilities, especially the HT's considering their size, so erring on the low Tx audio side is preferred at this point.  We would prefer to advise you to increase your audio rather than be blasted by the AGC fast attack times.

Details on the initial testing session with different radios and microphones

NOTES:  A HT was used for the Rx audio and VU meter which was calibrated for +3 dB for Touch Tone 5.  The TT level doesn't change when changing mic level or AGC enabled or disabled so that was a baseline which anyone can use for relative testing.  As TT levels are normally set at 2/3's of max dev for the channel bandwidth, the +3 dB VU was a reasonable target to get the audio down to.

Testing was done using all R01.08.xx firmware with AGC enabled, then disabled with gain levels set at +7 dB (TRBO default) and +4 dB using the  internal mic on the HT.  Next, using a mobile with the standard compact mic, then the Impress Touch Tone mic and lastly the Impress base mic.  TT and base mics typically in the Motorola line are very hot and tend to hear that pin fall to the floor from across the room so comments are included in this almost anecdotal test method.

If this topic seems worth more effort, I maybe try using a Sinadder 3 to interpret the TRBO audio as a  supplement the VU meter readings.  For now, waiting for feedback on what is currently here.

XPR-6500 HT (R01.08xx)

AGC enabled:  normal voice averaged +4 dB VU but easily went into the red +12 VU and distorted if I close talked the microphone.  My normal is 2-3" away and no direct breath puffs, all of which is problematic to maintain and provides the AGC opportunities to emit those piercing blasts of audio.

AGC enabled, Speaker/Mic:  + 3dB VU, 2" and 45 degrees, easy to go into red when close talking or directly facing mic to mouth.

AGC off,  +7 dB gain:  About the same as AGC enabled, easier to over drive but less likely the piercing blasts at the start of voice (compression ramping up when AGC is enabled).

AGC off, +4 dB gain:  Normal audio average was 0 dB VU when speaking 1" away from the mic, much harder to drive the radio into the red but could easily do that if I talked directly into the mic fairly loudly or blowing into the mic but it took affirmative effort and not likely to been done inadvertently.

AGC off, Speaker/Mic, +7 dB gain:  VU -4 dB VU, 2" and 45 degrees, about 0 dB VU close talking at 45 degrees, likely OK if you close-talk, less background noise in noisy areas.

AGC off, Speaker/Mic, +4 dB gain: -12 dB VU, 2" and 45 degrees,  0 dB VU when close talking and/or using louder voice, this for noisy environments.

XPR-4500 Mobile (R01.08xx)

AGC enabled, Standard Mic:  +4 dB VU, normal voice about 2" out and 45% to mic.  Easy to drive into the red though seems slightly less susceptible to that nasty piercing tendency.  Also mic slots face downward so holding the  so that you speak from above helps a bit and is fairly natural to do that anyway. 

AGC disabled, Standard Mic, +7dB:  +2 dB VU, normal voice at 2", all else about the same though less likely to be piercing than the HT's.  R01.08.10 noise suppression enabled reduced audio about 2 dB.

AGC disabled, Standard Mic, 4dB:  +0 dB VU, normal voice at 2", all else about the same.  R01.08.10 noise suppression enabled reduced audio about 2 dB.

AGC enabled, TT Mic:  About +3dB VU, interestingly, about the same audio level as the standard mic and even slightly less susceptible to breath puffs.  My experience anecdotally with these Impress mics is that they are hot and be like Motorola base mics that have that tendency to pick-up the drop of a pin.

AGC disabled, TT Mic, +7 dB gain:  +6 dB VU, at normal voice 2" away, 45 degrees.  R01.08.10 noise suppression enabled reduced audio about 6-10 dB.  A wild variation, I double checked this and cannot account for the large swing.

AGC disabled, TT Mic, +4 dB gain:  +2 dB VU, at normal voice 2" away, 45 degrees.  R01.08.10 noise suppression enabled reduced audio about 2 dB.  6-10 dB.  A wild variation, I double checked this.  A wild variation, I double checked this and cannot account for the large swing.

Set the level pot on the rear of the Desk Mic to about mid-range as a starting point

AGC enabled, Base Mic:  +2 dB VU, at about 8", again surprisingly low though the base mic tried to bring up the levels more noticeably than the TT or standard mic as is typical of Motorola desk mics.  2" easily put the VU into the red.  12" back averaged almost 0 dB. If high ambient noise, turn down the mic pot to 1/3 range, then up the CPS gain.

AGC disabled, Base Mic, +7 dB gain:  +6 dB VU, normal voice at about 12".  R01.08.10 noise suppression enabled had no change.

AGC disabled, Base Mic, +4 dB gain:  +2 dB VU normal voice at about 12".  Still can hit the red at 2" but lots of control by voice loudness or moving closer to the mic.  0 dB may be better for some.  R01.08.10 noise suppression enabled had no change.

User Comments:  Other users have reported good operation with these settings.  Remember, users voices and position to the mic tend to fit that user more so than the norm.  But we still want to provide this information for a more informed user.

Base Mic on a 43xx:  -15 dB gain, audio soft but worked well at 2" and much less ambient noise.

Contact DCI

Revised: 09/01/2015 10:15