Buffalo II I2S Interface (Again)
NOTE: Although this post reads like there is a problem with the DAC, what I am doing here is reporting a particular behavior of the DAC with certain (the most picky, I would say) settings are made in the registers. Choosing the right settings will allow the DAC to perform flawlessly (as you can see in the comments). Also I am particularly NOT saying that the Buffalo II implementation of the Sabre DAC is causing this behavior but that is the DAC I am currently using.
I spent quite a bit of time investigating the locking issue with the I2S interface of the Buffalo II (v1.0) DAC. Keep in mind that we want to use I2S because “conventional wisdom” says that I2S is better than SPDIF and in particular “it has less jitter”. Keep also in mind that the SPDIF interface in Buffalo works flawlessly with the DPLL setting at “Lowest” and that increasing the DPLL bandwidth will allow more jitter to pass through.
The “problem” is that the DAC (when using the I2S interface) will loose signal-lock which results in dropouts lasting a fraction of a second each. The severity of the problem depends on the DPLL bandwidth setting and the time since power-on of the DAC.
In my system, feeding the DAC with a Musiland Monitor USB interface, I was able to eliminate most of the dropouts by setting the DPLL bandwidth to “Medium-Low”. This setting is UP two notches from “Lowest” setting, which is the lowest bandwidth of a total of 7 possible settings (there is an 8th setting with zero bandwidth that prevents locking into the signal)
Additionally, when the DAC is first powered on, the dropouts are much worse, and even setting the DPLL bandwidth to “Highest” would NOT solve the problem. However, as the DAC “warms up”, the number of dropouts becomes smaller until reaching a steady state.
In my system, steady state is reached about ~15 minutes after power-on. At this time, setting the DPLL bandwidth to “Lowest” or “Low” would result in several dropouts within each song. Setting the DPLL bandwidth to “Medium-Low” would result in a dropout every few/many songs.
I did not test whether higher bandwidth would completely eliminate the dropouts but one report (see my previous post) indicate that even at this setting, the problem is not completely eliminated. However, setting the DPLL bandwidth to “Highest” may completely obliterate the advantages of using the I2S interface since the SPDIF interface works perfectly with the DPLL bandwidth set to “Lowest”
I can report that I2S at “medium-low” DPLL BW sounds no worse than SPDIF at “lowest” DPLL BW. In fact is seems to sound better, the music with “more sparkle”. One reader of this blog has indicated that the I2S interface sounds better for him (see previous post).
In any case, at least there is a quest to achieve “lowest” DPLL setting with I2S interface which is something that makes this hobby fun. I can see this happening through:
- More tweaking of the registers in the Sabre32 DAC
- More tweaking of the Musiland Board to lower the input jitter
- ESSTech tweaking the chip to figure out/fix why SPDIF can lock with “lowest” setting and I2S cannot
Also, I have improved the code to support I2S and enable more settings. I will publish that shortly after I clean it up. See my previous post on this subject to understand this issue some more.
Update 1/4/11: This material was posted previously but updated here with the latest information
Reports of having problems with I2S/DSD interface into Sabre32 DAC (the Sabre32 DAC implemented in different products, not just the Buffalo II DAC. So the “problem” is associated with the DAC chip)
To reiterate, the “problem” means using I2S and setting the DPLL bandwidth to “lowest”
- Hiface Evo [Link]
- TPA USB board based on the PCM2707 chip feeding Buffalo II DAC [Link]
- Musiland MINI, based on Spartan FPGA feeding Buffalo II DAC [This post]
- Teralink-X2 based on TENOR TE7022L and 1ppm TCXO feeding Buffalo II DAC [Link]
- AudioGD ESS-based DAC NFB-7 fed from Audio GD sources [Link]. Audio GD has discontinued the product right after launch
- “Manufacturer X” converting I2S into SPDIF before feeding the DAC [Link]
- SDTrans192 [Link] feeding modified Buffalo II DAC with better clocks and other mods. A good summary here [link]
- ElectrArt USB Interface and SACD players feeding Buffalo II DAC and Fidelix CAPRICE DAC : best DPLL bandwidth is medium-low [Link]
- SDTrans192 feeding a diy, highly customized implementation of Sabre32 DAC. This was previously reported as having no lock problem with lowest DPLL setting [Link]
- NeoY2K DAC [Link]
- XMOS USB 2.0 reference board (Link)
- exaU2I (Link). This basically proves that with the default setting at power on, the DPLL is using “best” and thus, no hiccups.
Reports of NOT having problems with I2S interface into Sabre DAC