On 11/28/06, <b class="gmail_sendername">Carlo Capocasa</b> <<a href="mailto:capocasa@gmx.net">capocasa@gmx.net</a>> wrote:<div><span class="gmail_quote"></span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
The irony of this is killing me. I had a singing capacitor in my<br>notebook computer, which I was able to solve using a load generator at a<br>low scheduling priority. However, that same capacitor is what had<br>triggered me to get a higher-end sound card in the first place.
<br><br>Now this higher end sound card has quite a loud hum when the phantom<br>power for its mic pre-amps is on. Interestingly, when I mix the signals<br>from both pre-amps by connecting them both to the same outputs in JACK,
<br>the noises from the Mics cancel each other out.<br><br>The load generator has no influence on the hum; however, the sampling<br>rate does. The higher the sampling rate the higher pitched the hum is.<br>The inverse is true for buffer size: The larger the buffer, the lower
<br>pitched the hum.<br><br>My current theory is this: Jack causes a surge of power in the CPU<br>through an interrupt. This surge gets transformed into current in the<br>grounding cable through electromagnetic induction, which in turn induces
<br>a current in the microphone pre-amps, which causes the hum. The hums can<br>cancel each other out because... uh, not the slightest on that one.<br><br>Help appreciated.<br><br>Carlo<br><br></blockquote></div><br>I also ran into some problem with my laptop. Those things are known to emit a lot of EM waves which easily get caught by cables transmitting asymmetric signals. When I switched all my connections between my sound card (RME) and my pre-amp (TL-Audio) to symmetric XLR, the hum disappeared.
<br>__________________<br>Marc-Olivier Barre,<br>(Markinoko).<br>