Working on my little computer that could broadcast to the neighborhood.
Reading lots about hum created by computerized audio sources.
Working on my little computer that could broadcast to the neighborhood.
Reading lots about hum created by computerized audio sources.
Anyone have any experience with USB audio devices (sound cards) and can speak of what they've heard with gear they own or tried?
Haven't decided on anything in the way of USB yet, so openminded.
I have zero experience with USB audio of any kind.
How sure are you that the hum in your audio card is caused by the computer?
Are you sure the hum is not being caused by the wiring or other equipment connected to the audio card?
I have had internal cards inside a computer interact with each other, but it wasn't hum but RF type buzzes and whistles.
I was able to re-arrange the cards for minimum interference, and I used a spare slot to install a 100% grounded slab of aluminum sheet metal, carefully arranged so it did not short anywhere.
If your USB device is actually the source of hum, maybe putting it in a grounded metal box would help.
A USB device is outside the computer, so maybe you can move it or other external components that might be too near by.
There are two usual sources of hum: ground loops in the audio chain and RF interacting with power supplies.
Audio should have a one point ground meaning that it is grounded at a single point. Often this is not practical and it has been reported that using a ground isolator (from Radio Shack) is a good solution.
RF can interact with power supplies which can cause hum, especially "wall warts". Solutions include using snap on ferrite rings on power leads but the most reliable solution is to keep wall warts and transmitters separated as far as practical. Sometimes just a few feet will work, other times larger distances are needed. Enclosing FM transmitters in a metal box usually helps. Not so much with AM since the signal is much stronger than FM.
That, in general, is an overview of the hum problems for part 15 stations but if you are having this problem there may be other causes.
Neil
There is one particular type of hum that has nothing to do with RF or ground loops.
It is generated by the computer itself.
When interfacing with outboard equipment to and from the computer's sound card, the external equipment may have too much input sensitivity, thus it is picking up internal noise in the sound card itself. This hum is like a spike type hum, in fact when viewing it on an o-scope, the waveform is NOT a sine wave hum, but more of a saw-tooth type waveform, and sounds almost as if the hum has a high end spike type sound with some noise floor added.
Typical fix to this is to use 1 to 1 isolation transformer or a ground loop eliminator box like those found at Radio Shack. Though it is a ground loop eliminator, it is actually functioning as an isolator for the "hot" side of the audio connections, and of course as well as the ground side of the audio connections. But it does eliminate that high pitch type hum.
RFB
My brother inlaw recently replaced his PC with a MAC. He gave me the "old" PC, much newer than any I have.
The motherboard sound card system will not allow recording audio played through the sound card such as a streaming audio file. I tried installing an internal PCI sound card, same thing.
I tried looping the speaker output to the sound card input with limited success.
So, I hooked up a USB sound card made by Berringer. Simple little gadget. L/R audio in, L/R audio out and a headphone monitor jack independent of the L/R audio out. Cost about $25.
Works fine. The noise floor is around -60db, typical for an inexpensive sound card. I looped the input to the output which allows recording of audio played through the sound card. The headphone output drives the amplified speakers.
The inputs are line level. To use a microphone would require a preamp or outboard mixer.
Glad to hear most folks aren't seeing real problems out of these USB sound devices. Unsure if it's just an older issue or diehard audio nuts or a case of a bad manufacturer or chip maker.
Have yet to test things here. Still in formulative stage rounding up parts and planning. Best to ask folks who are doing this already and not duplicate the problems.
Thanks @mram1500 for your input.
Good morning censoredSHIP....
Got to wondering, want to learn more about the world of USB audio devices....
What is the model of USB device you have?
Well so far Carl, I just have a no name Chinese un-brand. Actually have two different ones, but suspect probably the same chips and manufacturer.
Dirt cheap too < $10 each. Think they weren $5-$6 range a year ago when I started tinkering with them.
Might consider the fancier higher end models for tinkering later. Goal is to build and test rapidly and then improve things where feasible. There are tons of "high" end USB cards out there, but not financially available to many people today.
One of the cards looks very similar to this one:
http://www.ebay.com/itm/New-USB-2-0-3D-Virtual-Audio-Sound-Card-Adapter-Converter-7-1-CH-Mic-Speaker-/321022092999
Nice thing about USB is you can affordably run (given have CPU to do this) multiple cards. So in theory should be able to have one for line (phone, remote, etc), one for rendering final audio out to speakers and one for general mixing controls. That's my idea 🙂 Probably is overkill.
It's so interesting that such tiny plugins can convert digital to analog in both directions, and record/playback from the harddrive. I can understand wanting to try them out.
When the Amiga Computer was at the heart of our business GVP came out with an 8-bit analog/digital sound device that plugged into the serial port, and the crisp quality was amazing at the time.
The USB port has the whole thing down almost to the size of a smart card.
USB is super convenient - just plug and play typically with stuff like this. No nasty drives, complicated configs, etc.
The control software and getting it to work in conjunction with other cards at same time is a whole other story.
It's low cost too which is very important to most of us. Can afford to stock spares and double up on equipment.
My project, mates the USB sound card with an ARM based tiny computer (same general chip family as smartphones). Additionally bundling USB drive (flash) for OS install and file storage. Have to see how the USB performs with that all on the same bus. Should be fine for most uses though.
Looking at something the size of deck of cards but higher and with USB items hanging off it. So able to be stashed, stored, put in lots of places.
I plan on bugging folks here about their automation software for their stations, because that's my intended use for this. To replace the big PC that is so common and offer a sort of hybrid of the PC and a Barix unit.