- Support for 4x20 LCD Display and large number display
- Brightness and contrast adjustment with remote
- (OPUS/Wolfson WM8741) DAC volume control: remote and rotary encoder
- (OPUS/Wolfson WM8741) DAC random filter selection 1 to 5 with remote
- (OPUS/Wolfson WM8741) DAC upsampling selection (L, M, H -this is the OSR setting)
- I2C level shifting (5V to 3.3V)
- Optimized power-up sequence

Wednesday, November 18, 2009

Testing WM8741 filter setting

Some people can hear differences between the digital filters in the WM8741 DAC. In my setup, I can't really hear clear differences between the different filter settings, and up to now I had no way to test whether the different filters were being selected by the software in Arduino.

The good people at AMB did an excellent job in characterizing filters 1, 2, and 3 with different upsampling, and found that without upsampling (i.e., with 44.1KHz material), filters 1 and 2 will roll off at 15Khz as compared with filter 3 as shown in this picture:

I downloaded a 15 KHz test tone (from mosquito ringtones) and played it in a loop in iTunes. The output was set at 44.1 KHz and I set the OSR bit in the WM8741 to "high" (meaning do not use internal upsampling). Then I selected and compared filters 1, 2, 3. Indeed, you can hear an attenuation with filters 1 and 2 as compared to filter 3. Filter 1 is filter A, 2 is B and 3 is C.

Therefore the software is working. (Keep in mind that if you are an old guy, you will need to ask a kid to help you listen to the 15KHz test tone)

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