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Thread: Motorola ASTRO (Legacy) Radios: Optimize your audio

  1. #1
    Join Date
    Dec 21, 2011
    Thanked 8,680 Times in 2,388 Posts
    Country: Canada

    Default Motorola ASTRO (Legacy) Radios: Optimize your audio

    First, please see this related thread on ASTRO25-series audio enhancements.

    In April 2002, Motorola engineers released new firmware and a document explaining subscriber "Generalized Gain Control" and how to implement it.

    Motorola explains it best:


    If the customer complains of:
    – Low console audio,
    – Wide variation in received levels requiring excessive volume changes for comfort,
    – Excessively loud talkers,

    Generalized Gain Control can be used to reduce transmit level variations. This will result in more consistent receive volume levels.

    Before resorting to the GGC, all the level setting recommendations of PSB907B should be followed. Also, correct radio microphone usage should be encouraged (speaking directly into the microphone with the mouth about 2” away).


    Perhaps unrealized at the time, CGC (Audio AGC) would become the most important and beneficial enhancement to any analog or digital, conventional or trunked, radio system. It balances audio at the source: The user.

    Early ASTRO systems, regardless of whether they were IMBE or VSELP, sounded like absolute garbage. Harsh, but the truth. The terrible shrill-sounding (high-end) audio characteristics of DSP 6 firmware, combined with the lack of any amplitude-control of the transmitted audio, vastly contributed to end-user dissatisfaction with the whole digital-radio experience.

    The issue is/was so bad, some scanner-radio manufacturers decided to implement "Digital AGC" features into their products. This helped to alleviate some of the brutal-sounding audio on these systems. (If monitoring a system where subscriber-AGC has been implemented, be sure to disable the feature on your scanner-radio!)

    Motorola worked hard to improve the tone-balance (especially in later DSP 8 firmware) and came up with AGC. If you have a 1-Meg ASTRO Saber or ASTRO Spectra, or a XTS3000, and you're not running R07.xx.00 (portable) or R11.xx.00 (mobile) host firmware, with N/I08.xx.xx DSP firmware, then you must get a firmware update. The difference in both received and transmitted audio quality is night and day.

    (You're welcome to contact the technical team if you require a firmware update for any ASTRO/ASTRO25/APX radio.)

    Please read the attached PDF file for further technical information and a detailed explanation of how to utilize the AGC settings in your older ASTRO gear.

    The most common and effective setting for transmit-audio AGC (apply in RSS or CPS) is the following configuration:

    Gain Type: AGC
    Output Gain: 0dB
    Total Gain: +6dB

    This is the configuration I use, and it works fantastic!
    Attached Files Attached Files

  2. The Following 3 Users Say Thank You to Mars For This Useful Post:

    opfor2 (Nov 07, 2016)

  3. #2
    standardmissile No Longer Registered


    Thanks! My CVSD audio tests actually come out intelligible now, and APCO sounds absolutely gorgeous.

  4. #3
    Join Date
    Apr 09, 2012
    Thanked 694 Times in 258 Posts
    Country: Australia


    I just did a firmware upgrade for a local HAM here in Sydney - their radio was sounding like total ass on transmit, but received fine so they weren't even aware they had a problem.

    They gave the radio to me, the firmware was bumped, and the codeplug settings were changed to the reccomended settings of:-

    Gain Type: AGC
    Output Gain: 0dB
    Total Gain: +6dB

    The original settings were:- (LOL)

    Gain Type: Linear
    Output Gain: 0dB
    Total Gain: +12dB

    No wonder they sounded terrible on Tx!


  5. The Following 2 Users Say Thank You to MattSR For This Useful Post:

    Mars (Jun 06, 2019),opfor2 (Nov 07, 2016)