Yearly Archives: 2022

Running the MOTU M4 USB audio interface without bus power

The MOTU M4 is a high quality, yet relatively affordable USB audio interface with 2x XLR/TRS in, 2x TRS in, 2x TRS/RCA out, 2x TRS out, 1x headphone out, 1x MIDI in, 1x MIDI out. The M2 is very similar, just without the 2x TRS in and 2x TRS out. Judging by the firmware, I am tempted to claim that the M2 and M4 are technically identical, just with a different back panel with fewer connectors hooked up to the ADC/DAC.

Some high-end audio interfaces have a separate power input, but the M4 is exclusively bus-powered. In theory you only need the separate power supply when your computer does not supply enough power, but the M4 is well within the limits of what the specification guarantees. The M4 actually also has a standalone mode where you can use it as a mic preamp by connecting it to a USB power supply. However, like most audio interfaces, it has one power-related downside: it makes the speakers pop when it is turned off. Some people say it’s on the quieter end of the spectrum of audio interface popping, but I would rather have complete silence when I reboot or shut down my computer. Interestingly, MOTU managed to make it completely quiet when powering on. I tried a powered USB hub, but its power output is still controlled by the computer, so the interface loses power and the speakers pop when I reboot my computer.

There is a simple solution to this problem: the USB-C/PWR Splitter by 8086 Consultancy. You can use it to power the M4 from a USB power supply, but connect its data lines to your computer as usual. This solution may also work with some other USB interfaces, but it’s not guaranteed that the interface will keep its output powered when it loses the data connection to the computer.

There is also a significantly more expensive solution: the MOTU M6, which can optionally be powered by a separate but included power supply. You might also shop around for other audio interfaces with separate power connectors (Focusrite Scarlett 8i6 Gen3, Arturia MiniFuse 4, Universal Audio Volt 4), but it’s not guaranteed that all of them will keep running when they lose the data connection to the computer. I picked the MOTU M4 because its case and knobs are mostly metal. My previous audio interface had some parts made from soft-touch plastic, which after about a decade began getting stick and shedding drops of plasticizer, so I was not going to spend money again on soft-touch plastic like on the Arturia’s knobs.

Scientific Article: A thermalized electrokinetics model including stochastic reactions suitable for multiscale simulations of reaction-advection-diffusion systems

Dissertation: Lattice Boltzmann methods for microswimmers in complex environments

Abstract

This dissertation introduces, validates, and applies various models for the study of microswimmers, predominantly focusing on the development of lattice algorithms. The models are applicable to biological swimmers like bacteria, but also to artificial ones propelled via chemical reactions. The unifying theme is a complex fluidic environment, ranging from Newtonian single-component fluids, to electrolyte solutions, to viscoelastic media flowing through arbitrary geometries. A particular focus is placed on resolving each swimmer’s surface since the propulsion, or phoresis, originates from a small layer of fluid around it. Resolving the propulsion mechanism is necessary to accurately study hydrodynamic interactions with obstacles and other swimmers. It is also a prerequisite for the study of taxis, that is, alignment with an external field such as a nutrient gradient. Similarly, phoretic interactions can be investigated, like when a swimmer senses and avoids the trail where another swimmer has already depleted the fuel.

Update January 2024

Here is an updated PDF with all the preprint citations replaced with the published versions. This should make it easier to find all references via the DOI system.

thesis Download

Dell WD19TBS review

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Four years ago, I reviewed the Dell WD15 USB-C docking station for use with a MacBook Pro. It worked reasonably well, but not all of the USB ports worked and high resolutions didn’t work over DisplayPort. Also, over time it has become a bit unstable for me, requiring the USB-C cable to occasionally be unplugged and replugged, or even requiring the dock to be power-cycled. The latter is also necessary when switching between a Dell and a MacBook, which can be a bit annoying. I also noticed that the WD15’s firmware cannot be upgraded unless you use a Dell laptop from around 2017 — newer ones will try and fail, while non-Dell laptops won’t even run the updater.

Dell’s current docking solution is the WD19. It is available in three variants: the WD19S connects via USB-C, the WD19TBS connects via Thunderbolt or USB-C, and the WD19DCS connects to certain high-end Dell laptops via two USB-C cables. Conveniently, the WD19TBS is certified for use with Macs too. The WD19/WD19TB/WD19DC (without the “S” at the end) are identical, but do not have an audio output.

This review is going to be really short. The WD19 eliminates all the WD15’s flaws that I complained about. Dell provides good documentation that tells you what works via USB-C and what requires Thunderbolt, which resolutions you can get on how many video outputs, etc., so I am not going to repeat that here (the executive summary is that there are no surprises here).

The WD19 has one downside though: it has a fan. Mine turns on and spins up to relatively loud levels every couple hours for a few minutes, which I find quite annoying. Another WD19 I have used never spins up. I don’t really think the fan is even needed for regular usage unless you have a laptop that draws more than 80W of power. So if you’re feeling adventurous and want to void the warranty, open up the WD19 and disconnect the fan. Dell laptops will occasionally display a BIOS warning about a failed fan, but other than that it works fine and completely silent.

Firmware updates no longer require Windows or even a Dell laptop. You can apply them via fwupd on Linux too.