Jeroen's Project Journals

Way back in 2023, I wrote about the major issue with this project. To recap: the Teensy Audio library does all processing in 16-bits, which means volume control in the digital domain leads to noticeable loss of sound quality. I ended with the line “I might try to modify the mono-amps to a lower gain, and I’m also looking into ways to do the DSP in 32 bits. I’ll probably needto do both, I suspect.”. This turned out to be quite prophetic, as that is exactly what I ended up doing, although that second part took until this year.

When looking for displays to use in both the DSPDAC and Amplifier, I found a couple of 256×64, 2” OLED modules based on the SH1122 controller that looked perfect. Nice resolution, 16-level greyscale, small enough to fit the enclosure. I got them wired up, plugged in the u8g2 library, and they worked! Except for one rather glaring problem: the display was comically slow to update. I could literally watch the image being drawn from top to bottom, taking about half a second to complete.

While both the processor on the Teensy and the external DAC chips are 32-bit capable, I belatedly discovered the Teensy Audio Library is entirely 16-bit. This is quite unfortunate, as this has implications for the final sound quality.

Even before I started building the concrete subwoofer, I realized I didn’t have the audio gear to properly hook it up. For my PC I have a SMSL Q5 Pro DAC/Amplifier, which does have a subwoofer line-out but does not handle cross-over or any other kind of DSP. So I decided to do what every self-respecting maker would: build it myself. The result is this 4-channel USB DAC with DSP capabilities.