New to moode and having fun, but...

[Mellowship]

@Mellowship

I'm in basic agreement with Tim (of course ). Just wanted to add a few comments about your hardware environment.

1. Regarding the glitchy playback. It sounds like you might be suffering underruns. Have you looked at the logs for underrun messages?

While the RPi3B is a decent SBC, its USB/Ethernet subsystem is a known chokepoint. It's possible that reading data in from the USB HD and simultaneously writing high bit-rate data out to the USB DAC is challenging the throughput limit of the shared controller. One test of this hypothesis would be to try playing tracks from an external NAS and/or other computer via the WiFi interface and see if you still experience glitches. 

If this is the problem then you could move your music library to an external NAS or even try replacing the RPi3B with an RPi4B which has a superior interface subsystem. (Yeah, I know, the RPi4B is yet another SBC and also is more expensive. I prefer it but you could instead just buy another RPi3B to dedicate as your moOde player and repurpose the existing RPi3B and USB HD as your NAS.)

2. Regarding the Bluetooth performance. Since you are using a USB DAC I assume you don't have a HAT on your RPi3B, but what about a case? If the RPi3B is near or surrounded in metal, you may get poor or even no BT performance (WiFi too, but more so the BT). Same if the RPi3B is buried in the typical rat's nest of cables in a media center. 

Also, do you have lots of other 2.4GHz gear in the vicinity? Microwave oven, cordless phones, WiFi and/or Bluetooth devices? Any strong transmitter nearby can contribute to poor performance.

3. I haven't used Spotify in ways which would cast light on your podcast and downloaded libraries issue, so can't comment.

Regards,
Kent

PS - there are old audiophiles and then there are *old* audiophiles. 

<reminiscencing>
My first experience with recordings was playing my parents' 78s as a pre-teen in the early 1950s. These discs simply shattered if you dropped them so I had first to earn my folks' trust. Since the recording time per side was so short, you had to stack the record changer with a set of discs when you wanted to play a symphony and needed to reverse the stack halfway through. Over time you got so you could ignore the constant interruption and clatter of the disc changes. 

Fortunately they bought a new console with a built-in three-speed changer soon after I started listening and we could begin amassing 45rpm and 33rpm records. Then I built my own primitive stereo system with a "high-fidelity" Garand changer. This led first to my discovery of record shops and later of audio stores. What a life! 
</reminiscencing>

Thanks for your reply.

78 rpm shellac records... That's old indeed! ? I also had some trouble being granted the trust to play my older brother's 33s on the Pioneer turntable, so I had to use cassette tapes. When the Walkman fever came, I was already a master in compilations... 

Regarding the vicinity of the raspberry pi, it is on a shelf just above the WiFi router. So it could be it. The case is an official white and pink plastic one. 

Haven't been experiencing glitches lately and everything seems fine. But that's a good idea to get another pi to use as NAS. If I get a good deal on a used one (like I had with my current, 40€ for a complete kit of pi, case and power + 500gb hd) that's what I'll do. It would allow me to keep only one music collection and stream it to any device.