Hifiduino Code and Buffalo III DAC
HOW COMPATIBLE IS THE HIFIDUINO CODE WITH THE BUFFALO III DAC?
People have successfully used the HIFIDUINO code with the Buffalo III DAC, and I have generally said that “it should work”, but I had never tried to figure out whether there are any incompatibilities, inconsistencies or bugs when used with the Buffalo III DAC, primarily because I didn’t one have to test with.
I’ve now decided to do some theoretical study on how compatible is the HIFIDUINO code with at least the “commonly” (or default) STEREO or MONO configured Buffalo III DAC. I am doing this to satisfy my own curiosity and to give confidence and peace of mind to those using the code for the Buffalo III DAC, which I believe is now more widely used than the Buffalo II DAC. As audiophiles, we care as much about sound as the “perfection” of the audio chain :-)
BUFFALO III “DEFAULT” CONFIGURATION
Based on the BIII integration guide, the default STEREO configuration (jumpers, connections and dip-switch selection) for I2S and DSD is as such:
For reference, here is the configuration for Buffalo II on which I test my code. We will compare the Buffalo III input configuration with the input configuration of the Buffalo II DAC. If we find that the two are equivalent, then as far as the code is concerned, there is no incompatibilities to worry about. The code can’t tell whether it is controller a Buffalo II or Buffalo III DAC as they are based on the same chip and the only difference is how you configure the inputs.
ANALYSIS AND OBSERVATIONS
The first thing we observe is that the Bufalo III DAC default DSD configuration is “covered” by the BII input configuration. In other words, the wiring for the Bufalo III DAC for DSD is a subset of the wiring for the Buffalo II DAC. Both configurations require that you remap the inputs
How about for the I2S configuration?
Notice that the default Bufalo III DAC configuration for I2S does not require that the inputs be remapped. But for the DSD configuration, input remapping is required. Wouldn’t it be nice if for both configurations we can use the same “input remapped” setting? This would eliminate the need to be changing the input mapping configuration every time you switch between a PCM source to a DSD source
Thus, if we remap the inputs (which is just a software register setting), we can remove one of the jumpers and still feed all the internal DACs like this:
We notice that there is no use for Data 3; but we also know that there is no harm having a live signal on that pin (because the same thing happens in the BII without adverse effect) and thus, there should be no harm even if you leave the 3rd jumper in place.
With this equivalent configuration for the Buffalo III DAC for I2S, we also realize that it is covered by the Buffalo II input configuration.
Because in the default configuration, the Buffalo III DAC input wiring is equivalent to the wiring of Buffalo II DAC, the HIFIDUINO code is fully compatible with the default STEREO configuration of the Buffalo III DAC, whether in its I2S mode or in its DSD mode.
By extension, therefor, the code is also fully compatible for a DUAL MONO BUFFALO III configuration.
HOW ABOUT 8-CHANNEL MODE?
The first thing to do in order to support 8-channel is to undo the input remapping. This can be done in register 14:
|0|x|x|x|x|x|x|x| Source of DAC8 is DAC8 (D)
|1|x|x|x|x|x|x|x| Source of DAC8 is DAC6 (Use this to match BII input wiring)
|x|0|x|x|x|x|x|x| Source of DAC7 is DAC7 (D)
|x|1|x|x|x|x|x|x| Source of DAC7 is DAC5 (Use this to match BII input wiring)
|x|x|0|x|x|x|x|x| Source of DAC4 is DAC4 (D)
|x|x|1|x|x|x|x|x| Source of DAC4 is DAC2 (Use this to match BII input wiring)
|x|x|x|0|x|x|x|x| Source of DAC3 is DAC3 (D)
|x|x|x|1|x|x|x|x| Source of DAC3 is DAC1 (Use this to match BII input wiring)
Quantizer bit depth also affects input remapping as follows:
As you increase the quantizer bit size, the DAC internally turns off the digital sections for half of the DACs and replicates the output to all the analog sections of the DACs. Further increase of the quantizer bit size further turns off the digital sections for half of the remainder DACs resulting in using only one quarter of the digital sections of the internal DACs. Thus, whereas all the analog sections are always fully utilized, the number of channels available in the DAC depends on the quantizer setting as follows:
||Quantizer||Input Channels Used
|1||6-bit||8 (All)||8×1 – 8-Channle|
|2||7-bit||8 (All)||8×1 – 8-Channel|
|3||8-bi||4 (#1,#2,#5,#6)||4×2 – 4-Channel|
|4||9-bit||2 (#1 and #2)||2×4 -Stereo|
This means that the only allowable quantizer setting for 8-channel is 6-bit and 7-bit. The current code supports all settings so in order to configure for 8-channle, you just make the correct selection in the user interface.
Therefor, the code can be made fully compatible with 8-channel by just making a small change in the code. When i get a chance I’ll incorporate this into the code and make it an option.