System AMDM (Autonomous Multimedia Display) often becomes a headache for drivers and fleet owners when it comes to the basic configuration. Unlike premium minibuses, where the sound is adjusted by professionals, in standard city transport you have to figure it out yourself. Understanding how they work chords (in this context, sound combinations and sequences of signals) and equalizer settings can turn the rumble of a diesel engine into an acceptable background.
Many people mistakenly believe that it is impossible to achieve high-quality sound in a regular bus due to engine noise and body vibrations. However, the correct distribution of frequencies through the AMDM interface allows you to compensate for low frequencies and highlight the announcer's voice or music. The key point is not the volume, but the balance, which is achieved through the settings menu.
Before you start deep tuning the AMDM system, be sure to take a photo of the current screen parameters - this will help you quickly return to factory settings if the sound gets worse.
In this article we will look at how to adapt standard settings to the realities of city noise. You will learn which frequencies need to be raised and which ones should be cut so that passengers hear announcements clearly and the music does not irritate the ears. Chords System notifications can also be configured so that they are audible to the driver, but do not frighten people in the cabin.
Basic audio architecture in a standard bus
The acoustic environment inside the bus is extremely aggressive. Low-frequency engine hum, squealing brakes and tire noise create a constant background noise that drowns out the mid-range frequencies. The AMDM system in its basic configuration often has a flat amplitude-frequency response, which makes the sound “mushy.”
First you need to understand what equipment you are dealing with. In most cases, this is a head unit with limited functionality and speakers scattered throughout the cabin. Channel distribution This is critical: if all speakers play in the same phase, echo effects may occur.
- 🔊 Low frequencies are often lost due to vibration of glass and panels.
- 📢 Mid frequencies (voice) should be prioritized for ads.
- 🎵 High frequencies in cheap speakers can give an unpleasant metallic sound.
You shouldn’t expect studio quality from a standard system, but improving speech intelligibility is a completely solvable task. The main thing is not to try to compensate for engine noise by simply increasing the volume, this will only lead to distortion and rapid driver fatigue.
AMDM interface: navigation and main sections
Access to sound settings in the AMDM system is usually hidden in the engineering menu or requires activation of the administrator mode. The standard user interface is often limited to volume control only. To access advanced settings, you must use a special combination of buttons or enter a code.
Most often the path looks like this: go to Settings → System → Audio. Some software modifications require you to click on the firmware version five times in a row. Once you enter the menu, you will see EQ, Balance, and Fader options.
Code for Admin Access: *#8899# or Long Press'Menu' +'Vol+'It is important not to blindly change values in hidden sections. Gain Options (Gain) is better not to touch without measuring equipment, since exceeding them can lead to burnout of the speakers. Focus on EQ and crossovers.
What happens if you change the crossover settings?
If you set the crossover frequency incorrectly, the subwoofer (if there is one) may try to reproduce high frequencies, and the tweeters may try to reproduce low frequencies. This will lead to wheezing and possible equipment failure.
Equalizer settings: combating engine noise
The most important part of tuning is adjusting the frequency response. The bus engine generates powerful noise ranging from 40 Hz to 200 Hz. In order for the speaker's voice to be heard, you need to carefully raise the mid frequencies without increasing the hum.
Use a parametric equalizer if available in your version of AMDM. If only graphical (sliders) are available, work carefully. Center frequencies (about 1-3 kHz) are responsible for speech intelligibility; they can be raised by 2-3 dB.
- 📉 Turn down the 60 Hz slider to reduce engine noise.
- 📈 Raise 1000 Hz for clearer dispatcher voice.
- 🔇 Cut everything above 12-14 kHz to remove the hiss of old speakers.
Don't forget that there are many hard surfaces on the bus that reflect sound. Excessive raising of high frequencies will create a “ringing can” effect. It's better to make the sound a little warmer and softer than harsh and bright.
The optimal setting for a bus is a V-curve with a dip in the low frequencies and a smooth rise in the mids to cut through background noise.
Table of recommended frequencies for different conditions
To simplify the setup, we provide a table with basic values. These parameters are suitable for most standard configurations with a 10-20 W dynamic head. Remember that each bus is unique and the values may require (fine tuning).
| Range (Hz) | Recommendation | Effect | Level (dB) |
|---|---|---|---|
| 40 - 80 | Cut | Removes engine noise | -3 to -6 |
| 200 - 400 | Neutral | The physicality of sound | 0 |
| 800 - 1500 | Boost | Speech clarity | +2 to +4 |
| 4000 - 6000 | Easy lift | Presence | +1 to +2 |
| > 10000 | Roll-off | Removes hiss | -2 |
Use this data as a starting point. Run a test track or ad recording and listen to the results at different stops. At idle and during acceleration, the sound may be perceived differently due to changes in engine speed.
Synchronization and latency issues
In long buses or articulated models (accordions) the problem of sound desynchronization often occurs. Passengers in the rear hear the announcement later than those standing next to the driver. The AMDM system may not have a built-in delay to compensate for this effect.
If there is an option in the menu Delay or Time Alignment, it can be used. However, budget systems do not have such a function. In this case, you have to resort to tricks: for example, turning off the speakers in the front part of the cabin when working on long routes, so that the sound comes out evenly from the center.
⚠️ Attention: An attempt to programmatically increase the delay beyond limits may lead to desynchronization of video and audio in commercials. The video will open the mouth, and the sound will come late.
It's also worth checking the wires. Long cables to the rear speakers may lose signal, especially high frequencies. Using a power amplifier in the middle of the cabin can solve the problem of signal attenuation.
☑️ Sound system diagnostics
Audio system maintenance in winter
Winter is a difficult time for bus electronics. Temperature changes, condensation and voltage surges in the on-board network (especially when starting a cold engine) affect the operation of the AMDM. Speaker cones become hard in the cold and can crack when the volume is suddenly increased.
During the cold season, it is recommended not to turn on music at full volume for the first 10-15 minutes of engine operation. Let the system warm up. Also check the contacts: oxidation of the connectors due to moisture is a common cause of lost sound.
Condensation inside the speakers can cause short-term wheezing that goes away after warming up. If the wheezing does not go away, the speaker is most likely damaged by moisture and needs to be replaced. Don't try to blow dry them on high heat.
FAQ: Frequently asked questions
How to reset AMDM settings to factory settings if the sound is gone?
Usually in the settings menu there is an item Factory Reset or Reset settings. If the menu is not accessible, try holding down the power button for 10-15 seconds or find a hidden Reset button on the device (often a paperclip is required).
Why is there a whistling sound in the speakers when braking?
This is a sign of poor grounding or interference from the generator. Check the fastening of the negative wire of the head unit to the body. Old high-voltage ignition system wires can also create a problem.
Is it possible to connect an external amplifier to a standard AMDM?
Yes, if the head unit has a linear output (Line Out). If you don't have one, you can use a High-Low Converter, which connects to the wires going to the speakers.
What should I do if the sound only disappears in announcements, but the music is playing?
Most likely, the channel balance is off or a specific input in the AMDM mixer is disabled. Check the settings in the section Audio Sources or Mixer. Make sure the "Announcement" or "Mic" channel is not muted.