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New protos tested and ready to ship!

A project log for Teensy Super Audio Board

Professional quality, 24 bit, 192kHz audio breakout board for Teensy 3.x, Raspberry Pi, and more.

rf-william-hollenderRF William Hollender 08/12/2015 at 16:190 Comments

I was finally able to (mostly) complete all three new prototypes Monday night, and started testing last night.

I powered up the first board with the Teensy all ready to go, and ... nothing. Turns out I had completely forgotten to load the I2C bus pull-up resistors (oops!). I loaded those on the boards, tried the first board again, and still nothing. The two other boards did communicate just fine, so I think that I broke something when I powered up the first board with no pullups (hopefully just the I2C isolator).

Unfortunately, this means that Hackaday is getting all three of my working prototypes!

I did do some quick tests with the two new boards to make sure that they were performing well. The first board had measured loopback THD+N of -98.945dB for the left channel and -98.837dB for the right. The second board measured -97.95dB for the left channel and -99.612dB for the right.

Here's a shot of one of the new boards under test with a Teensy:

I also finally tried actually playing music through the board hooked up to a Raspberry Pi. One thing that I didn't anticipate was the difficulty of finding an MP3 with a sample rate of 48kHz.

One of the design tradeoffs with using the digital isolators between the codec and the controller is that it's not possible to switch the codec between master and slave mode because the isolators are unidirectional. The isolators are set up such that all the I2S interface clocks are sent from the codec to the controller, and not the other way around, so the codec has to be the interface master, and can't be the slave.

One benefit of the codec being the master is that the interface clocks are generated directly from the crystal on the board, so there is very little jitter. The downside is that the board can only handle 48kHz, 96kHz, and 192kHz because the CS4272 doesn't have a PLL to generate other frequencies (like the normal consumer audio rate of 44.1kHz).

Anyway, I didn't have my Raspberry Pi set up with any audio tools that could re-sample normal 44.1kHz mp3's to the required 48kHz, so my wife and I scrambled to find a file that used right rate. The only one we could find happened to be "Party in the USA" by Miley Cyrus.

Here's a quick video clip of it playing out through some old computer speakers I had lying around. I didn't know my wife was filming, so I wasn't ready for her question. This is more of an outtake :) :

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