A/D conversion and Hum

B

Bacha

New member
I currently have a sat-receiver connected to the analogue line-in socket of my iMac to make audio recordings (no video). The performance of the A/D conversion by the sound card in the iMac is quite good, but there is one problem: there remains a small hum in combination with medium wave radio signals (obviously I tried all kinds of things regarding mains connections and grounding). When the iMac is not connected, there is no hum and no radio signal at all.

The situation irritates me so much that I am considering a PC with a decent sound card. The question is, which combination to use? I expect the sound card is most important? Should it be outboard?

In this forum I read about the LynxOne. A bit expensive, though. It has 4-channels. Is there an alternative with 2-channels: 1 in and 1 out? Or are there other ways to go?

Any help is appreciated!

/Bacha
 
you know.. pretty much its like this. My old atari is better than an iMac.

Sell now. get a PC.

Dont get ANY onboard video or sound. What kind of quality are you looking for? There is a range, all of which are better than your iMac.

xoxo
 
Xoxo,

I just want to record sat-radio in good quality; that's not really CD-quality, but it's coming near to it. I just want to get rid of the hum and RF signals (not to mention the mouse clicks and disk spinning).

The sat-receiver has a SP-DIF optical output. Maybe that's the way to go?

/bacha
 
a 4 ch. sound card means 4 in / 4 out.

it wouldn't be to expensive to buy a decent stereo i/o card i guess. search the forum for exact specs.

greetz guhlenn
 
If you are getting a hum, it is probably due to a grounding problem with your power. Can't give you a cure but I think it is a place to start.

Do you get this hum if you are watching tv going thru your a/v system.

The s/pdif option would be a good choice if you have the similar connection on your sound card. My only thought on that is if you wanted to hook up your sat system and listen to 5.1 surround, you will need your s/pdif to hook it up to your receiver.
 
if you had a SBLIVE, it has a SPIDIF in, and I gather that it would have sufficient quality for your needs...I would troubleshoot this hm, first, tho. Are you sure its the Computer?? cuz you could get a PC, and find out that the hum is from your reciever... But if your using a spidif connection, there should be no hum-style interference. the interference would be jitter-style.

xoxo
 
I'm rather sure the hum is from the mac: when disconnected from the mac, there is no hum at all (no rf interference as well). When connected, there is a small hum. When the mac is turn on the hum (up to 100 Hz; we have 50 Hz mains), increases. Also mouse clicks and disk head movements can be heard (and also rf interference).

Perhaps a dedicated PCI SP-DIF card will do.

/bacha
 
Ummmmmmmm

Have you made sure that your computer and the sattelite system are plugged into the same AC power circuit? If they are two different ones, that would constitute the ground loop that JC talked about above. If this is the case, plug them both into the same AC outlet, also making sure that ANYTHING else, like home stereos, TV, etc...that might be hooked up to the SAT. system is on the same outlet too.

Bet that clears it all up.

Ed
 
I'm afraid I did that from the beginning, Ed. It reduces 95 or more percent of the hum. A fraction remains...

/Bacha
 
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