MOTOTRBO radios, poor audio AGC performance - SOLVED

An audio fix utility is now available. Link here (http://communications.support/threads/10106-AUDIO-FIX-for-all-MOTOTRBO-subscriber-radios)

It is a well-known fact MOTOTRBO radios have TERRIBLE audio AGC performance on both analog and digital. The DMR-MARC group even goes so far as to require all members on their network kindly disable AGC on subscriber radios, as AGC distorts the audio beyond belief.

Both original and the newer 2.0 series TRBO line have this problem. To date, there has been no resolution, other than suggestions to muck around with linear audio gain levels until you get it "just right". But this is inconsistent and everyone has different speaking habits. One setting does not fit all.

One of the projects I undertook this winter was to identify and correct the audio issues which affect the TRBO platform. I firmly believe aside from RF coverage, the most important thing on a system is the audio. If subscriber (or dispatcher) audio is poor, it causes many issues. Some of those issues are:



- Unintelligibly (having to repeat oneself);
- User/dispatcher listening fatigue;
- Disinterest in the system/technology (hams);
- Profitability (users will go elsewhere if they perceive your system audio sucks);
- Distraction (users having to adjust volume levels constantly).

I'm sure there's more. High-quality system audio is critical, especially when working with low-bitrate codecs such as AMBE+2, which is used in DMR.

Here's what I observed with Motorola's TRBO products:

- EXTREMELY LOUD, out-of-control audio amplitude; (Remember the ASTRO DSP6 days?);
- Distortion/clipping;
- AGC not working properly. It was making loud audio LOUDER, not quieter;
- Poor dynamic range of gain levels. (AGC doesn't really seem to work at all)

There are several hidden settings/values within the radio codeplug which control AGC operation and audio amplitude. These settings are NOT accessible via CPS or any "depot" software which is floating around. These are factory values. The settings (and default values in 2.0 radios, including the LITE series) are:


RC_NUMBEROFCLIPPEDSAMPLES 7 (Firmware limit: 0-31)
RC_MINUMUMHWGAINADJUSTMENT 247 (Firmware limit: 244-250)
RC_SATURATIONTHRESHOLD 250 (Firmware limit: 0-255)
RC_DMICREFPL -22 (Firmware limit: 252-33022 [not sure how -22 relates to these values]
RC_AMICREFPL -24 (Firmware limit: 252-33022 [not sure how -24 relates to these values]

(I have also seen -20 and -20 for both DMICREFPL and AMICREFPL in certain firmware versions)


There are many other hidden settings, but only these are to blame for the poor TX audio in Motorola's 2.0 series radios. Broken down, they are:

RC_NUMBEROFCLIPPEDSAMPLES (Number of Clipped Samples): This is the number of samples in a defined period of time, which exceed the "Saturation Threshold" level (amplitude) which will then cause the AGC (a DSP function) to kick in. Think of this as a trigger.

RC_MINUMUMHWGAINADJUSTMENT (Minimum Hardware Gain Adjustment): This is the minimum amount of gain applied to the audio when the AGC circuit is active.

RC_SATURATIONTHRESHOLD (Saturation Threshold): This is the predefined value (amplitude) which the number of clipped samples must exceed, before the AGC circuit is triggered.

RC_DMICREFPL (Digital Mic. AGC Reference Power Level): This is the MASTER mic gain which is referenced while operating in digital mode. Think of this value as a fixed-resistor on the audio input of the DSP. It affects the amplitude of signals before they're processed by the AMBE+2 codec.

RC_AMICREFPL (Analog Mic. AGC Reference Power Level): This is the MASTER mic gain which is referenced while operating in analog mode. Think of this value as a fixed-resistor on the audio input of the DSP. It affects the amplitude of signals being sent to the modulator of the radio while operating in FM mode. Note: This is NOT deviation control.

The default settings which Motorola has programmed into the codeplug are sub-optimal. In fact, they're terrible. I don't need to tell the thousands of people who are using TRBO products in a professional or hobbyist capacity, just how loud and distorted the audio can be. We all know. Unfortunately, Motorola doesn't seem to think it's an issue or they would've changed it by now.

I have modified the default settings so they function properly. Here's what I've done in each area:

RC_NUMBEROFCLIPPEDSAMPLES: I've reduced this trigger from 7, down to 2. As a result, AGC triggers faster. (Do not confuse this with AGC attack time)

RC_MINUMUMHWGAINADJUSTMENT: This minimum and maximum gain settings do not have enough dynamic range between them. I have reduced minimum gain from 247 to 244.

RC_SATURATIONTHRESHOLD: I've lowered the saturation threshold from 250 to 248. This allows the AGC circuit to trigger on lower amplitude. (once clipped samples threshold is reached)

RC_DMICREFPL: This is the most significant change of all. I have lowered the master digital audio gain from -20 to -30. This dramatically reduces the distortion caused in both linear and AGC audio modes. A night-and-day improvement. This alone, cures the majority of the distortion issue.

RC_AMICREFPL: The master audio gain on analog is also lowered from -20 to -29. I found analog audio -- especially on the mobile radios, to be too loud with AGC engaged. Linear audio is also somewhat distorted. Changing this gain setting is a big improvement.

In the original MOTOTRBO radios (XPR 4000 and 6000 series, aka DM/DP 3000 series), there are only two settings which are of interest:


RC_DMICREFPL: -22
RC_AMICREFPL: -24

Again, these are the master mic gain levels. I will be experimenting with them to determine the optimal settings and will update this thread. I do not have any 4000/6000 (DM/DP 3000 series) radios here to experiment with at the moment.

I will be posting some audio samples (hopefully today) of the dramatic before/after changes. I will also submit these findings to Motorola, but I somehow doubt they'll take an interest. If that's the case, I am happy to modify (for a reasonable fee) anyones' radio codeplug with these changes, so they can have better sounding audio on DMR-MARC. All distortion and loud artifacts (including initial SUPER LOUD BLAAAAAAAAAARGH on keyup, which ramps down after a second or two) is resolved. Believe me, I know exactly how bad these issues have been for the last few years. It was total garbage. That's why I got to the bottom of it and completely resolved the issue.

Codeplug mods are permanent (you can read/write with CPS) until the next firmware update, which will default any changes back to factory settings.

Digital Ham Radio / Amateur Radio

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