I received my DAC+ DSP yesterday and immediately started configuring it. Installation was however non trivial so here is my rundown of what I had to do.
When first booted the system I didn't get any controls at all in alsamixer even though I followed the instructions in the documentation:
I added dtoverlay=hifiberry-dac to /boot/config.txt and removed the driver fot he built in audio.
I then tried to control the volume as described in https://www.hifiberry.com/build/documentation/mixer-controls-on-the-hifiberry-boards/ but that does not work for this board.
Instead I reverted to google and found a Hifiberry GitHub repository that got me part of the way: https://github.com/hifiberry/hifiberry-dsp
The default raspbian installation does however not include some of the needed libs and the build fails without them.
I had to install: libxslt1-dev libxml2-dev zlib1g-dev
After that the build succeeded and I could get the server up and running. Setting the volume did however not work until I refreshed the DSP with the default configuration that I found under https://github.com/hifiberry/hifiberry-dsp/tree/master/sample_files/xml
The control interface in alsamixer did show up but had no effect, and dsptoolkit complained too.
I used dacdsp-default.xml
dsptoolkit install-profile dacdsp-default.xml
That did however not work out of the box. To get it working I had to symlink ~/.dsptoolkit to ~/.hifiberry and create a copy of dacdsp-default.xml called dsp-program.xml within that directory.
I have no idea if that was the right way to do things, but It at least made it possible to reload the dsp. I then ran dsptoolkit store.
Now the volume control works.
Shairport-sync does however complain about the also-mixer not supporting a dB scale:
"note: the hardware mixer specified -- "DSPVolume" -- does not have a dB volume scale."
Which means it silently (unless you run it using -vvv) reverts to a software volume control. Changing volume using airplay does not have any impact on alsamixer or dsptoolkit get-volume.
Spotifyd Is not capable of lower the volume all the way down. Spotify indicates that the volume is as low as it can bre, but alsamixer is still at around 37% and the output is still active.
I was pleasantly surprised that the TOSLINK audio and the audio coming from the raspberry Pi was mixed and that the volume control is controlling the mixed output.
Coming from an IQaudio Pi DAC Pro I noticed a significantly higher noice floor. There is clearly noticeable noise coming from the speakers using the same power supply and nothing else connected to the PI other then the RCA-cables and a TOSLINK.
Before changing the volume I also had a very bright sound coming from the speakers, not at all what I normally hear. Almost (or actually) distorted. Bass response was weak as well.
As soon as I changed volume I feel it balanced out a bit, but the bass response still feel suppressed.
I created a EQ-file based on https://github.com/hifiberry/hifiberry-dsp/blob/master/sample_files/roomeq-daniel.txt
Which only included an EQ at 90Hz with a Q value of 1 and a boost of 6dB. That helped a bit but its obviously not tuned. It is more in line with what I get from any other DAC using these speakers. (I have the DSP connected to active studio monitors Dynaudio BM5AmkII.)
All in all, a bit disappointed with the sound quality.
The DAC+ DSP solved a real problem for me, getting wired audio from the TV to my monitors (using TOSLINK), but the performance is honestly not that great.
Anyway, that's my initial experience with the DAC+ DSP.
If anyone can give me advice on how to solve the outstanding issues I would be glad to hear it.
(Shairport-sync requires a db scale in alsa, spotifyd not going all the way to 0% (-60dB(?), simplified installation, sound quality)