unusual noise from soundcard input, even when muted.

4 replies [Last post]
veda_sticks
User offline. Last seen 8 hours 48 min ago. Offline
Joined: 2011-03-11
Posts:

I recently started to use my internel sound cards inputs to record audio. and have noticed that there is an unusuall noise floor. its very unbalanced aswell, having a significantly higher level on the right side than the left. even with the input level set at the min for the sound card its still present. this noise isnt audible.

its also still present if i mute the input.

if i load jamin and rout the input into jamin to look at it with the HDEQ, it shows up as very low frequency noise. the highest level revestering at the lowevst frequency which is about 25hz which tails of to about 30hz.

this recordings look biased towards the right side even though they are coming in dead centre from the source. playing back recordings also shows this bias to the right.

Is this system noise? or just due to the poor built in sound circutity of my cheap motherboard. its just weird that this noise is still present even when muting the line inputs.

the exact same noise is still present if i switch to the mic input.

seablade
User offline. Last seen 4 hours 11 min ago. Offline
Joined: 2007-01-22
Posts:

I would place money on cheap built in sound card. While the specific to low frequency interference is a new one to me, built in sound cards just are not built for good quality recording, thus why external interfaces are so common. Not only are they better quality components, but they also get the AD/DA process outside of the box the computer is in, which significantly reduces likelihood of interference from those sources.

Seablade

linuxdsp
linuxdsp's picture
User offline. Last seen 8 hours 36 sec ago. Offline
Joined: 2009-02-04
Posts:

I would agree with seablade, that the quality of (most) internal sound cards is not as good as that of (most) external or add-on interfaces, and is likely the cause of your problem, however I would also say that my experience with jamin leads me to believe it is not the best piece of software to try and conduct measurements with. The recent tests I've done with jamin seem to suggest that jamin has some kind of bug that causes it to add at least as much noise as the average internal sound interface to anything that passes through it (there was significant noise in the presence of signal even for a pure digital tone input). I would recommend something like baudline if you want to do genuinely accurate measurements.

veda_sticks
User offline. Last seen 8 hours 48 min ago. Offline
Joined: 2011-03-11
Posts:

thanks for the input. i have no doubt that my internel sound card is probably the most likely culprit. considering the motherboard cost me a mere £30.

The interference is noticable visually before any jamin stage. it shows up as a constant signal in ardour when a new track is created and the line or mic inputs are routed to that track. If i insert jamin on the new track, it shows up as a very low requency signal, its not much but its enough to show up. it also shows up in freqy tweak.

after reading through some unreleated posts about spread spectrum settings in bios im wondering if this is creating teh noise. Its been so long since ive looked at my bios i cant remember if these settings are disabled. ill need to check this on next reboot.

However, despite the very cheap nature of my motherboard, i am very pleased at the quality of recording i have managed to achieve just plugging straight in from a sound craft series 4 mixing consol ( home made xlr to mini jack cable)

ill try baudline and see what that shows, though compairing the input shown just in the meters in ardour with what jamin shows it seems somwhat accurate. Ill also check my spread spectrum settings as this could well be the culprit.

Using my pc as a recording source was only a temp solution as my digital recorder died on me. Normaly i would use that then import the wave file for editing.

Mike Johnson 1962
User offline. Last seen 2 years 50 weeks ago. Offline
Joined: 2011-04-02
Posts:

I have a similar problem from my internal sound card!! It's quiet when booted in XP but after 5 mins on Ubuntu it sounds like an old valve radio searching for a signal!! That happens all the time not just in Ardour