On Thu, Jun 18, 2009 at 10:59:16AM +0000, Jacob Meuser wrote: > I played with this a bit and was unable to get rid of the pop. I > left outputs muted, and still got the noise. as far as I can tell, > the pop happens when the codec is powered up. I think the codec has a "virtual ground" tied halfway between 5V and 0V or whatever its power supply is. The output is then connected to the real output with a capacitor to avoid a 2.5V DC offset at the output (this is commonly done when you only have a single supply but need a split one).
When the codec is powered up, all of it is at 0V. The virtual ground will rise to 2.5V, causing a very loud spike as the output capacitor charges. It's not possible to mute this except with a mute transistor after the output capacitor (haven't seen any sound card with one of those) or a very slow-rising power supply, making the narrow, tall spike into a wide, low pulse that you can't easily hear. Surely not somehing you can fix without physically poking the hardware, though probably not very difficult if the noise is really annoying. -- Jussi Peltola
