Crackly Sound – solutions?

[raoulangel]

Hey all.. Enulation works great, but the sound coming out of my (powered) speakers is so crackly at times.. Also there is a hum that the screen produces but I don’t think there’s anything I can do about that. I am more concerned with the crackling during gameplay. Would I need to get a separate audio board for this or are there settings in the ALSAMIXER or ALSACTL that will fix it? Or is it just a limitation of this particular version of MAME4ALL? Please, any tested working solutions would be very helpful! Thanks

[evilllama]

I can’t help but wonder if this is a hardware issue, not a software one.

First off, if you are using the jack rather than HDMI, I think I know where you are getting the humming sound from. Are you able to use the HDMI output for sound, or is this a cabinet (or old TV) installation? With my home-made cabinet, I am using a new style tv at 90^ because the audio jack and crt/projector video seems to throw too much interference for the sound to be crystal clear. But the hum does make it sound more authentic…

I have a set of powered speakers that I was going to use on my cabinet that produced almost identical issues. It picked up a hum from the projector within the cabinet (foil fixed that issue until I figured out how to turn the video output 90^ and grabbed a new flat) and it was crackling on specific heavy load conditions where the driver (coil of the speaker) was under heavy stress.

After a a while, I added an 12v light strand into the power circuit for my speakers and draped the inside a reflective cabinet in the top behind the PAC MAN translucent so that it would light up when the machine was on. This allowed me to SEE the amount of power consumption on the power circuit. When the cracking started, the light was either out or dull and flashing like a weak strobe light. Turns out, there just was not enough juice (with the power supply that came with the speakers) to handle the load, and no it was not because of the lights. I removed the lights and took out my trusty multimeter to confirm. I switched them out for a sound bar that I modified (as I had installed a flat screen).

I have no hum and no crackling. Though now I miss the humming because it made me feel 14 years old again with the humming of the arcade cabinet… nostalgia…

I would try a different set of speakers to see if the issue persists. If the issue is worse or better, I think you can bet the speakers you have are underpowered (as far as cracking). As far as the humming (and assuming you are using the audio jack), I would try moving the speakers (and wires) around to see if there is any change in the intensity of the humming. interference can be picked up by the coils, but also by the wires of the speakers.

OH, and could you please also let us know what your set up is currently? RPI version, monitor type, speaker set up or rather what you are using for your audio outputs… In this situation, it COULD be just a hardware issue. Or not. :)

[raoulangel]

Actually, it’s a mini-arcade cab, used to be a Coleco Zaxxon Tabletop. Barely 6 x 7 x 8 inside, just enough room for the screen, video board, Pi, speakers, Mini-Pac kb encoder and wires!! So everything is close range… (pic attached) I will try and see if I add one of the Pi Audio breakout boards if it will help.

[raoulangel]

Pi 2 version B, Adafruit svga screen with video driver board (using HDMI), 3-watt USB-powered speakers with 3.5mm jack, Ultimarc Mini-pac, wired to Arcade Mini stick and 14 buttons… Powered by the built in 4 “D” battery compartment…

[raoulangel]

I moved the speakers to 10 inches from the Pi unit outside the container and it still hums as long as the screen is on.

[evilllama]

THAT is a tough installation. Proximity make diagnosis more of an issue. Should you try the breakout board yet render no change, you may find trying a new set of speakers or (if you did what I think you have here) moving the power supply out of the cabinet. I *think* from what I see, you have the plug inside the cab. The humming sound might be fixed by moving the power supply outside the cabinet. Also, you want to insure that you separate the audio and power lines. For example, if you run power through the right side of the cab, make sure the audio lines are run on the left side. They should never run together side by side, be close to one another, and (as they say in Ghostbusters) never cross the streams! The audio line are likely to pick up distortion (humming) if you touch the two types of lines.

RE crackling, the speakers you are using a VERY small if you are using stock locations (again assuming). Considering the emulator is typically emulating larger cabinets, turning down the volume might be a small step in the right direction. I believe the only speakers that would fit in the stock location would be constructed more like a headphone speaker. The coil is not designed for the type of frequency response that the emulator is trying to force. IE bass sounds of an explosion will sound garbled because there is not enough play in the mini coil to extend and there is not enough cone space nor surround to allow the extension needed to recreate the frequency without “bottoming out” causing distortion (the garble or crackling sounds).

Much like putting a sub-woofer in a car, under-powering the driver would also cause this issue should the cone and coil allow for the necessary movement as there is not enough “juice” to force the extension repeatedly. IE 30 cycles over a 3 second period requires the load of almost double the specs of the driver to CLEANLY produce or continue to produce the vibrations…. or on the most basic level, 100W 4ohm speaker needs almost 200W @ XOhms (depending on bridge and a million other factors) to produce and sustain the sound at full volume (considering the line level provided is not trowing amplified distortion… nor the amplifier). Not a huge issue here, but again… If you have only one gallon of water, you can not fill a 500 gallon pool.

Sorry, was trying not to go technical, but if the new board fails to fix the issue, you may want to consider the above. ;)

[raoulangel]

The Pi is supposed to be portable for a reason.. I am using it for my project because of it’s ability to provide the flexibility without the space requirements. The Power is supplied by 4 “D” batteries in the orioginal battery compartment under the unit. Cannot remove that. The extenal power plugs into a barrel connector at the side of the unit, the wires are attached internally to the power ports of the Pi and the screen. The speakers are powered from the Pi USB ports, and so will the LED lights for the Marquee. The interference was there even when everything was outside the enclosure laid out on the table.

[evilllama]

Interesting. I want to know what happens when you get the new board. Considering the configuration, wiring, and the fact that even with everything out of case, and you still have the humming sound…

I am going to looking into your display a little more. Think I might pick one up for testing. What one are you using? By spec, they all seem to be shielded and should not throw interference (but separating the sound and video devices would have lessened the hum if that was the issue). I also can’t think of a reason for it to send back interference through the board(s). Even if it is under-powered at 6v dc… but that would be the crackle issue, not the humming.

At this point, less an oscilloscope, I can’t for the life of me think of an easy way to test the standard jack (which you are taking out of the equation with the new board). Curious…

[raoulangel]

http://www.adafruit.com/products/1680?gclid=CjwKEAiAx4anBRDz6JLYjMDxoQYSJAA4loRmoLVRhPFbLwNPwPXg1x6GzMnd_uCHsDHw1-4bTNY4SxoCTY3w_wcB

Adafruit 5″ 800×480 LCD with 40 pin connector

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