My USB is fluttering. I’ve got an ART USB Dual Pre I’ve used for many years (meaning, it’s not new), and recently, even with nothing plugged into it and the input volumes turned all the way down, it’s producing a fluttering sound.
“Get a new USB interface” - I’m not against doing that, but I’d still like to know what’s going on.
“We’re discussing Audacity, not external hardware.” - I know, but I’d still like to know what’s going on.
“What version of Audacity, etc etc?” - 3.7.4 running on an Acer laptop, Windows 10 home, but I’m not sure what difference that would make, and I’d still like to know what’s going on.
Noisy USB power is also the 1st thing I thought of.
USB power is notoriously noisy (depending on the computer) which is no problem for digital but it sometimes gets into the analog electronics (depending on the device’s filtering) and the high-gain of a microphone preamp (or phono preamp) amplifies it.
I’ve also heard of cell phone interference causing problems with audio interfaces so if your phone is nearby try taking it out of the room.
Whenever I throw away a broken device with a USB type AC adapter, I always keep the adapter. I have a whole box full of them.
I recently got a digital oscilloscope and decided to look at each one of them, with and without a load. Most of the name brand, recently purchased power supplies are very jittery. The USB standard allows voltages of plus or minus 5%. To make up for voltage loss, they have started slightly overcharging up to the 5% allowed. The power supply then compensates by slightly undercharging, many times a second, causing the jitter. If my theory is wrong, someone will certainly point it out.
So the “good” power supplies have the worst jitter, and the older ones are under-voltage, but have a very steady sine wave. The best one I have came from a really terrible pet watering fountain that broke within days. It turned out the power supply was better than the product.
Interesting!!! I assumed a good USB power supply would be better than most computers. But of course you can’t use a separate USB power supply with a USB interface (unless you build an adapter cable). Luckily, the ART has other power options.
@Trebor : Ah-HA!! There’s a new WiFi router in the “studio”, I think all the USB-interface recordings I’ve made since it was installed were done in another room.
USB Power: I was thinking of that, too, but nothing had changed from pre-noise to current-noise. And yes, I just-now tried a 9v battery, but it didn’t change the noise level. (Using a previous laptop of mine, all USB-interface recordings had to be done without the noisy AC adapter.)