Noise disappears (ultrasonic?) when the phone’s 1.73A demand is added. Result: Loud SMP switching noise when power bank is under low load. Anker 5V.mp3 Actions: During the test we repeatedly plug/unplug a phone which draws an additional 1.73A. Test 3 – Anker 6-way mains USB power brick. Result: The unbearable sound of the computer “thinking”.
They’re all the same in this regard despite drawing power from different parts of the motherboard internally. Test 2 – Motherboard USB Motherboard 5V.mp3 It doesn’t matter which USB socket, rear or front nor USB 2/3/3.1. Test 1 - Baseline Baseline.mp3 No power to speakers. In a known-good and well-used configuration that is completely free from the type of interference we’re interested in.
Focusrite Scarlett 2i2 (coincidentally) at 192KHz/24bit. Recording: Behringer ECM8000 reference mic positioned almost in contact with speaker cone. Audio from the rear 3.5mm speaker jack of a Gigabyte Aorus x570 Master motherboard. Why? Because they exhibit precisely the problem of interest out of the box. No volume control, so permanently pegged at 100% volume. Power via a USB-A and audio via a 3.5mm jack. Can detect power supply interference on Mars and beyond. Playback: Really, desperately cheap USB-powered analog PC speakers. This setup is not intended to precisely replicate Dave Jones’s problem, instead a quick-and-dirty demo that I happened to have lying around. Everything else remains entirely consistent between takes. The only factor changing between these recordings is the source of 5V USB power. The following are real-world examples of several forms of audio interference which may occur when utilising USB power at one or more points in an audio signal chain. TL DR: Source of USB power can introduce catastrophic interference to USB-powered analog audio devices dependent on ground?/earth?/0V?/5V? referencing between connected devices and USB power sources. All provided such that somebody facing similar problems might have an “ah ha!” moment, potentially saving further headache. Not trying to teach anybody how to suck eggs. Everything based on 20+ years audio-visual engineering experience in broadcast/film/recording studio. Hello again, Disclaimer: Not an electrical engineer.
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