DAC discussions

[RPI4 Rambler]

moOde is a server using MPD as the music server engine. MPD supports the tags listed in the following document https://www.musicpd.org/doc/html/protocol.html#tags. The "Extra metadata" option in Appearance just displays some of the tags under the Cover art.

The Library in moOde uses a subset of the MPD supported tags as follows;

Code:

file
track
title
disc
artist
albumartist
composer
comment
date (or MusicBrainZ OriginalDate or OriginalReleaseDate)
time
album
genre
Last-Modified

moOde works well for most collections but due to the way the Library is generated it will not work well for really big collections. You would be better off using another music server and client system for example one of the UPnP based control points like Kazoo and a UPnP AV media server.

Thanks Tim. 
Off topic. Why do I persist with Moode? Well, first of all I like the things you have accomplished with Moode; it's left-field compared to other existing streaming solutions. Being an audiophile (not of the flat earth variety), I hate how much some (most) manufacturers charge for streaming devices. 
So, I took the left field approach. I spent a lot of time with daphile, unfortunately only available on x86 architecture but running even on 20+ years, quite low-powered old PC's or laptops. However, one ends up with an large form factor compared to RPI. 
My next stop was the Raspberry. I tried systems like Rune, piCorePlayer, Volumio, Raspian, RoPieee and others. Of all these systems I regard Volumio as your biggest "rival" though its creator, Michelangelo, has assembled a development team around him and is now focusing on the commercial side of things. But I do also have an RPI3B+ as well as an RPI4, running Volumio for the exact same content. Volumio has a real different approach to indexing, namely using mpd directly in conjunction with node.js (node Red?). Indexing takes a real long time with CPU loads frequently over >100%. With Volumio you really do need to edit mpd.conf to suit a large library; otherwise it will crash (guaranteed). 

By letting Moode and others do their own indexing, extra functionality becomes possible.

Then there are commercial products (music server systems) based on the RPI. Two (at least) stand out for me: Bryston's music server, and Pro-ject's Stream Box S2 Ultra designed by the famous John Westlake. Pro-ject's system uses an industrial version of the RPI. The cost of these commercial products is many times higher than the components that make up the cost of a Moode based system.

I do own expensive audio hardware (though nothing over the top) and wanted to prove that, when it comes to streaming, it does NOT have to cost the world AND that such an RPI system can hold its own in an otherwise expensive audio hardware environment. Cut to the chase: both system CAN hold their own in such an environment! 

Crucial in an RPI based system is the DAC that is being used either as a HAT or a USB DAC. Forget the usual HATS though (Allo, Justboom, HifiBerry etc) and generally any DAC equipped with TI's 51xx DAC chip. The problem with a really good DAC, is the limited Linux support for DAC's. Some Linux drivers (such as for Marantz Ruby / SA-12, and drivers for Pioneer, otherwise very good streamers) are totally CRAP. This is a big problem; it's widely held that Linux has excellent support for UAC 2.0 DACs, FORGET it! Unfortunately, for reasons beyond my understanding, particularly the 'good' drivers don't make it to the Linux kernel while the crappy ones do. BTW: it's relatively unknown that Windows 10, from a particular version onward, supports UAC 2.0 as well. 

For a HAT, I can strongly recommend (UGeek) Aoide's DAC II HAT though one would need customized versions of Moode or Volumio (no kernel support). You will need to get these custom Moode and Volumio versions from Github or Sourceforge. With USB DAC's you don't have that problem but you'll probably need the RPI4 (because finally USB is independent from Ethernet so no more stuttering and other digital artifacts). The problem with USB DAC's is the developer's willingness to implement a matching driver if the DAC is not kernel supported or when it is, it may be crap. Those kernel driver also often omit DSD, so that DoP is the only option. However, this creates substantial stream overhead and is limited to DSD128, if I'm not mistaken.
Aoide's DAC I mentioned handles resolutions up to and including DxD (PCM 384KHz) and DSD256 (11,2 MHz). Now that seems pretty high, but for computers that is really peanuts.
With Moode I use a Topping D10 USB DAC (same format support), an excellent little DAC for very little money. I will be upgrading to Topping's E30 (PCM 768KHz, DSD 22.6 MHz, preamp etc. (http://www.tpdz.net/productinfo/434825.html)) shortly, though, hoping that it will be supported by Moode.

In conclusion, if server systems can handle such "large" libraries on comparable hardware (or even less powerful CPU's), Moode and Volumio should be able to do so too, maybe by letting Moode etc. leave the indexing and presentation to those server systems. I can envision an extension in Minimserver or a special (customized) version of it to do so, with the extra functionality mentioned earlier. All in the spirit of open source. But I have no idea if such a solution would be viable architecturally, or workload intensive for the developers.

Cheers,
marco