This post is in many ways a continuation of the HiFiBerry DAC2 HD measurements presented last time with the devices sent to me by Doug Gardner for testing. For some background, this DSP Add-on is related to the BeoCreate project which was documented in this 2018 thesis in collaboration with Bang & Olufsen. The idea was to create an open-source system to allow consumers to build or update their own loudspeakers to be active devices. It looks like this DSP Add-On board leverages that software to do its magic.
As you can see in the thesis, the final BeoCreate product was a board which included 4-channel amplified outputs, digital S/PDIF input and output, DAC, and of course the programmable DSP subsystem. A Raspberry Pi could be added to provide network streaming capabilities.
For completeness, I want to mention that this DSP Add-On is also compatible with HiFiBerry's DAC2 Pro (~US$50-60) board. Notice that the DAC2 Pro is a less expensive DAC than the DAC2 HD and sports headphone out. The converter chip seems to be the TI PCM5122 (same as previous gen DAC+ Pro) based on what's listed in the specs sheet but I have not seen confirmation that is indeed the case.
Due to the low contrast and size of the markings on the chip, I literally needed to use a magnifying glass to check on the component label to confirm the DSP processor!
Remember that this is a low-power DSP chip so there are limitations to the complexity of the types of programs it can run in the 8kWord program memory. Having said this, there is a lot of flexibility to be had if one has the knowledge to mess around with DSP programming because the folks at HiFiBerry have opened up the system. One could program different "DSP profiles" - here are instructions on how to do this with design/compilation in SigmaStudio and upload to the add-on board over the network connection (access the file upload at: http://your_DSP_IP/misc/dspparamreader). And here's a DSP profile example to build from.
Clearly there is a lot to learn if you want to wade into this and I'll leave that to the experts. :-)
The built-in DSP profiles can be found in the Sound --> DSP Programs menu item which looks like this currently:
|Notice under the Listening Mode, you can quickly select one of 4 presets which can be customized. Very cool way to switch between EQ settings.|
I. "CORE" MEASUREMENTS
II. DSP FUNCTIONS & PERFORMANCE
|USB microphone to the left over the "Sweet spot", the Raspberry Pi 3 B+ "Touch" with HiFiBerry DAC2 HD+DSP is the bright screen on top of my Technics SL-1200 turntable.|
"Even giving the DSP module an advantage with higher volume didn't result in a preference for the DSP module. To me the DSP module made things sound different even though I was not using any filters or other EQ settings. It's not that it sounded bad. Just different. Not as clear."
That was my impression as well with "Listening Mode" set to "Optimal" and EQs all turned off before running the bench tests above. There was a subtle hint of lost upper end detail when listening to a track like Steve Winwood's "Higher Love" (Back In The High Life, DR16, 1986). For example that dynamic snare drum intro sounded a bit more "distant". I wonder if this might be due to the earlier roll-off with the DSP from 10kHz dipping to -1.5dB by 20kHz as opposed to the native DAC2 HD which stays flat and even accentuates 20kHz by about +0.25dB.
Otherwise, I thought the playback with DSP attached sounded good when I'm not being ultra picky and obsessing about the sound on and off. Remember that the point of having the DSP board is to purposely change the sound!
I think for many users, the "Room Compensation" feature will be of interest. It's easy to set-up and my miniDSP UMIK-1 microphone was detected and measurements proceeded without fuss. The results were quite good for literally about 5 minutes of work!
With the room EQ on, I listened to good 'ol Rebecca Pidgeon's "Spanish Harlem" (The Raven) to make sure the bass line was smooth (it was). Likewise, I listened to the plucked bass on Jennifer Warnes' "Ballad of the Runaway Horse" (Famous Blue Raincoat) again showing that it was better controlled than without the correction. Then I moved on to some familiar albums like Patricia Barber's Verse, Johnny Cash's American IV and Depeche Mode's Violator. A nice enjoyable evening of listening...
Sounds good folks, and certainly in my room, the DSP did the job of taming the frequency response without fuss. I like how the software gives the option of various types of compensation like "Bass only" (EQ affecting <300Hz), or the other options allowing EQ of higher frequencies. Soundstage was appropriately wide without any hint of constraint running through the processor, low-level details still sounded good, and even if there might be audible resolution loss in an A-B comparison, the sound was "natural" and I was not distracted by any sense of artificiality. Ultimately, I did have fun listening with the DSP on and that's the most important thing when it comes to this subjective portion of the review.
|Very cool seeing the Room Compensation EQ curve on the Raspberry Pi touchscreen. BTW, this is the calculated "Reflective Room" correction which tones down the treble a bit.|