Raspberry Pi HDMI audio vs USB CPU use

Quick note after some experiments last night. Not completely scientific, but enough to show a trend. I set out to compare CPU usage of the Pi running Volumio, upsampling lossless 44.1KHz 16bit stereo with ‘fastest sinc’ to 192KHz 32-bit stereo.

Streaming to the USB uses between 70 and 90% CPU. Streaming to the HDMI output uses 95% and more! Audio gets choppy in the latter case even without other processes getting in the way, whereas the former only gets choppy when the Pi happens to try and update the MPD database at the same time.

Wonder if anyone knows why onboard streaming should use so much extra CPU time to do the same work, and whether I2C suffers the same fate? Not sure I want to spend on a custom DAC if the current EMU 0202USB is more efficient?

Mike Oldfield: Tubular Bells

Don’t worry, I’m not going to do another review of this album. Many of us have read too many of them by now and my conclusion is that it’s something that one either “gets” or doesn’t. Instead I’d like to offer an insight on my experience of the album as a musical piece.

It’s an album I’ve always wanted to understand, and perhaps even grow to like, yet until this evening I had never heard it in a context or from a source that does it justice. I’ve owned a copy on CD since around 1990 I think, when I first became sentient and started to realise I love music. I remember getting that CD home and trying to listen to it on headphones and just… hated every moment of it. It wasn’t that the music itself was uninspiring, or that it needed concentration to really get the most out of, it was more that I felt I simply couldn’t hear enough of what it was made of for it to make sense. Perhaps this then was the start of my interest in audio?

Fast-forwarding through memories of several life stages accompanied by several audio playback systems through the last 20 years or so, up to the present moment. I find I have on the shelf a “well-loved” 1980’s pressing of the album on 12″ vinyl. My head hurts, life is what I might call “full” right now and some escapism is most welcome. So I put this on the deck and let it play out.

And I’m absolutely gobsmacked. For the first time I feel like I’m actually hearing the work. I can hear the timbre of the instruments and the arrangements. I can feel moods change, and I can appreciate the random non sequiturs that actually add to the intended mood rather than distracting away from it. The work feels right. And so I shut my eyes, listen, and am taken on an obscure journey that has completely set me to rights. Just wonderful.