Stereo jack Audio "Hum"

[cito]

on command line I don't get the Hum problem

but when I load XBMC, (all XBMC distros, rasbmc, xbian, openelec or XBMC on top of Rasbian all do the same)

and play audio through the stereo jack when I pause a video or music playing in xbmc I hear a hum it almost sounds like an old 60hz hum, but as I change menus go from video to music or whatever the thumping hum changes

so a popup info the hum will go to a higher pitch hum and sounds like a vibrating pulsing hum, then when I close the info popup and go to main screen the hum slows down to a slow pulsing hum

I've tried different speakers and all do the same thing.

If I play the movie from command line with omxplayer no problem
if I play mp3 from command line with mplayer no problem other than initital LOUD POP at start of song/movie and LOUD POP BANG at end of movie/song.


My main problem is that darn hum, it makes xbmc or audio in xwindows impossible with the stereo output.

My televisions are old my living room tv only has composite input and coax input

my television in my bedroom has just 1 coax input which I have to use a special cable box from comcast for that one.

only hdmi input I have is I am using a computer LCD screen but the LCD screen has no speakers. So I can't use the HDMI for audio. and looking up HDMI audio extractors they cost 100 bucks and higher to turn hdmi port into a stereo jack.

I tried headphones and even usb headphones but with the XBMC interface open there is a hum that corresponds to the xbmc menus

it's almost as if there is a filter missing from the stereo jack on the board. Or maybe I got a bad board.

any idea for a fix? or is it a bad board?

[PeteBremer]

I don't think you have a bad board. I've seen this happen on a lot of PCs and media devices over the years. It's just that the audio jack is picking up feedback from the display. Are the audio and video cables running close together in parallel (or touching)? Do you have the volume set to a very high level that might amplify imperfections in the electrical isolation of the board's components? When I've heard this happening it's usually been when I have the volume at or near maximum, while no audio playback is running. I have a desktop PC where this is fairly annoying, and I can toggle the behavior by turning the connected monitor off and back on.

Pete

[KenT]

Agree with Pete sounds like the audio amp is picking up the frame rate signal from the composite out. In addition to Pete's suggestion check the screen on the audio cable, are its connections loose, is it good quality. Also check the earth pin connections of mains plugs.

[redhawk]

Humming could be an indications of a power supply with poor ripple rejection, if you have another power supply I would swap it out and try that.

Richard S.

[ski522]

I've seen hum induced by the CPU running at higher utilization which resonates into the analog cable as well and might explain why you don't hear it on command line, but do in XBMC which tends to run the CPU at +50% utilization!

[mahjongg]

Perhaps your TV isn't grounded, and leaks some mains to its chassis, and GND line. If the hum stops if you pull the HDMI plug then that might be the cause.
Try grounding your TV.

[cito]

I'm using the much linked and power supply posted on the main site here: http://youtu.be/pDA7MxFtoS0

I have tested other power supplies, even plugging the Pi into a New Trent USB Battery Pack to see if battery power would fix the issue.

4 seperate power supplies and still have same HUM


Its not plugged into a tv, my only tv I own only has a coax input, no composite.


I have it plugged via HDMI to a 24" LG LCD screen with no built in speakers

I run my computer speakers which are Altec Lansing 2.1 setup to the stereo jack, the Altec Lansings have 3 inputs

So I have my gaming pc on 1 input - stereo cable 3.5mm male to male on my pc sound card

i have 1 on my ipod touch - stereo cable 3.5mm male to make on my ipod touch headphone jack

and just plugged in a 3rd to my raspberry pi,

and it hums like mad when I use any GUI as mentioned in first post.

I've unplugged all devices in the altec lansings and plugged just the Pi in, same thing hum with a GUI,

there is no hum playing music/movies from command line

only hum from GUI's and when you mouse over the GUI you hear the hum frequency change.

I've swapped cables, I've moved the Pi far away as i could from any source, also the Pi has a custom case so it's not laying in the open, and the case claims to help block RFI.

it's something on the board cause command line the stereo jack is clean when playing audio from mp3's, streaming from my radio station I own, or movies with omxplayer.

but any GUI i get the hums and change of hum frequency when windows popup or menus change.

I'm not sure what else to try, I've tried using different male to male 3.5mm stereo cables to plug into different speakers no change

I've tried unplugging the pi from network to rule out wirless or ethernet interference, no change


I don't know

I dont have a TV that can use the Pi


my TV in my living room is a 38" RCA that only has COAX inputs that we have comcast cable with, it's basic cable so they have a set top box that screws into the coax on the tv.

We never upgraded cause we dont plan to ever buy new tv's since we watch movies on our LCD screens, we are now 95% streaming online and only reason there is still basic cable is for local channels which I'm soon to have those turned off

But the Pi does not get plugged to any tv cause it physically cant

It's plugged into a LG computer monitor.

I have 3 LCD screens and I've tried all 3 and the stereo jack still gives vibrating hums at different frequency based on what GUI window is on screen.

I have nothing that accepts HDMI audio, since no LCD computer screen has speakers

I just have 3 sets of 2.1 type stereo computer speakers on 3 pc's and all 3 give that hum with the GUI up.

but playing from command line is clean.

thats why I'm thinking there is some bad on my board, some IF filter isn't working or fell off, or didn't get added to the board.

I've got no idea how to filter the sound of the XBMC or X windows Interface hums from the stereo audio

[PeteBremer]

Sounds like you've covered all your bases power supply wise, the battery test ends any question about the hum being introduced by the power source. Does the hum go away if you power down the display that the GUI is running on? If not, it would seem pretty likely to be something on the Pi, as long as there isn't anything else plugged in at the time. I'd want to do this -

1) boot the Pi powered from the battery pack and get into XBMC or what ever gives you the best humming

2) disconnect the keyboard, mouse, USB hub etc - everything but the speakers and the display

3) Power off the display or better yet unplug the HDMI to the display, keeping the PI powered up, leaving just the audio - If there is still a hum it's got to be coming from some component in the Pi.

Anything other than that would be pretty out there, a ham radio operator blasting your house with RF? Your house is a deep space gamma ray magnet? Radon gas decaying all around you at an alarming rate?

Pete

[cito]

haha yea, it's pretty weird.

if I am on the console only, so boot to Rasbian and use mplayer or omxplayer for music and movies then there is no hum whatsoever. the only thing is a pop at the start and pop when it ends (which is what most everyone is getting on the stereo jack anyhow).

so console based there is no problems at all, it's only when a gui is started.

So I tested again using my New Trent 11000mah battery pack I bought a year ago for my iPod Touch since I play a lot of 3d games the 11,000mah battery pack lets me play 3d games for days without needing to recharge the ipod touch. So that is what I've used to power the RasPi when I'm "mobile" or "testing"

So I've unplugged the "Plugables" 7 port 3am powered hub that was advertised on the main page a while back I posted link to their youtube vid in a previous post that is the exact hub I'm using to power it.

But I just plugged in the New Trent 11,000mah battery pack, I then unplugged the LCD screen removing HDMI plug from the case.

Only thing plugged in is speakers plugged into stereo jack, Cat-5 Ethernet cable instead of wireless going from PI to router, and New Trent battery pack.

I knew exactly when XBMC was loaded, cause as it was booting up when the sound driver was initialized I heard a faint "pop" as I always do when it boots and initializes the sound "card" so to speak.

But I could then tell exactly when XBMC was loaded as all the sudden a low rumbling hum could be heard.

I plugged in a keyboard and pressing left and right arrows which in my "mind's eye" i know im switching menus on the screen I can hear the hum resonance or frequency change as I'm scrolling menus.

That is just battery pack plugged into pi, speakers plugged into stereo jack and I did test it with and without ethernet plugged in.


I have the clear case and I took some photos of my Raspberry PI and put them on my Flickr stream

here is my Raspberry Pi photo set: http://www.flickr.com/photos/qoaa/sets/ ... 136696321/

I don't own a usb sound card so I'm gonna see about ordering a cheap one and testing it out.

I wish it was cheaper to split the audio off the HDMI port but HDMI Audio extractors the cheapest I've found is $120 on Ebay from China and it's a little white box you plug in HDMI cable from the source and it splits it into a HDMI video out to go back to your monitor/tv and has Stereo 3.5mm audio jack. Thus turning HDMI audio into analog stereo jack audio. But it's $120 bucks for the gadget from China


I don't mind running audio and movies from command line, Heck my main linux box is a Slackware linux distro and I've been a Slackware guy since the days of linux 2.0.25 kernel So I'm a "command line junky" for the most part, with my windows box for gaming.

Just found the hum odd. I'm googling trying to see if there is a in line filter I could try using, or perhaps see if I can figure a way to build one myself.

My idea would be build a filter that plugs into the stereo jack then you plug the speakers into the filter and it works like a bandpass filter.

I am an Amateur Radio operator, but all my rigs are off. That was the very very first thing I checked cause for my early 90's I was passing out RF bandpass filters to my neighbors so they wouldn't get mad at me running 500 watts on 20 meters

[PeteBremer]

I'm a newly minted ham myself. I got my ticket this past March. Anyway, if you'd want to split the HDMI into right and left audio and VGA you could try this item from monoprice, it's $38.25, so not too steep.

http://www.monoprice.com/products/produ ... 1&format=2

Pete

[cito]

btw just to update

earlier this week I did a apt-get upgrade

and noticed 2 firmware packages being updated for the sound on raspbian at least

I forget the 2 it was was firmware-blah

now there is no longer any hum on the stereo jack in raspbian for me, and no more popping at all when changing songs in mpg123 or using the X windows media app Smplayer!

no hum or popping in xbmc menus either now

so for me the last firmware updates earlier this week and the update to alsa as well 1 or all played a part in fixing the issue.

no more pops, hums or crackles for me using raspbian and the stereo out jack.

plugged into altec lansing 2.1 setup 2 speakers with a subwoofer, the speakers are actually about 15 years old bought them loooong time ago but they sounded soooo great I've never replaced them.

just wanted to update the post that my audio probs were fixed with recent firmware and alsa updates from apt-get upgrade