Do I need a new sound card?

October 15, 2005 5:50 PM

Crackly sound in my amplifier...

I've just bought a stereo amplifier (sherwood brand) second hand, to replace an old Aiwa brand one. This is what I use to drive a set of large Bang & Olufsen speakers connected to my computer.

The sound is definitely more crisp - on the old amp I had to turn the bass way down and the treble waaaay up to get clear sound, and there was an annoying hiss at all volumes.

Now I'm noticing some tracks on my computer have a crackly sound, particularly with loud and high pitch sounds. However, while experimenting with this I hooked up my MP3 player to the stereo using the same inputs as I had used for the computer, and it sounds great at any volume.

I've played with input volume and so forth, and it seems that my computer's output is where the problem exists. I have a motherboard mounted soundcard.

Am I hearing crackly noises that were always present but lost to the old amplifier? Would a new soundcard be better? Any recommendations? I'm not a major audophile, but I do like clean sound.

posted by tomble to technology (7 comments total)

Get out a multimeter, and look for some small DC offset in the source that is crackling. Line inputs, and in particular, cheap carbon volume pots, do not like DC.
posted by Triode at 6:14 PM on October 15, 2005

The old Aiwa may have had DC-blocking caps on the inputs, and the Sherwood may not. Also, the PC has a switching power supply with multiple pos and neg voltages, all of which is fundamentally referenced to safety ground at the power supply. Since the Sherwood is AC powered, it too is ground ref'd, and there may be a few volts difference between the ground in the PC and the amp. The mp3 player is slient because it is battery powered, and is therefore unreferenced to the ground of the PC.
posted by Triode at 6:19 PM on October 15, 2005

Yeah, DC Offset. I ended up building two headphone amps for the Grados -- one with caps on the input to block the DC offset from the computer, one without for everything else.

This page discusses the issues with caps on the inputs. The best answer might be a little insert plug with the caps that you can attach to the computer and leave there.
posted by eriko at 6:49 PM on October 15, 2005

Ooh, good call on the inline adaptors, eriko. Pulling a value out of thin air, a 0.47 uF film cap on each channel would probably work nicely. Go with a bigger value if it rolls off the bass.
posted by Triode at 8:22 PM on October 15, 2005

My vote is that the sound card is picking up interference from one of the many high speed digital circuits on the motherboard, and it was always there but your previous amp did not have the frequency response to make it noticeable.

You will know this is the case if the noise varies depending on what the computer is doing. Try listening to a track of music with everything but the player app closed. Now play the same track again but have heavy disk IO or CPU usage going on in the background (for example, while defragging a hard drive and compressing a RAR file.) If the interference is noticably worse, then it's interference and no DC blocking caps will do anything about it.

If that's the case then shop around for a replacement sound card that has better isolation. The perfect one would not even be a card but an external device with its own powersupply. But I think you can still get clean sound from a properly shielded soundcard.
posted by Rhomboid at 8:25 PM on October 15, 2005

One other source of crackling with loud sounds is clipping. Try turning down the PCM volume (not the main volume, though that may also help) on your computer and then cranking up the volume knob on the amp.

I find with some loud tracks that I can't have the PCM volume beyond about 75% otherwise it causes clipping in the latter stages of the sound card. This is totally unrelated to what amp is connected; the difference is probably just that you couldn't hear it with the old one.
posted by polyglot at 10:43 PM on October 15, 2005

If you want good audio from your computer, get an external interface. M-Audio has a bewildering number of good choices.
posted by omnidrew at 8:23 AM on October 16, 2005