Possible RPi FLAC issues


First post here. Hello everyone.

Even though I am a huge fan of vinyl records, I do have a collection of few hundreds of CDs which I enjoy listening to. Moneywise, it wouldn’t be wise to buy all those albums on vinyl. My CD player went bust, however, and I decided to give up on repairing it – instead, I am going to buy a DAC. I just need to something to feed it with FLACs.

Using my old laptop is out of question – it is noisy and I myself spend too much time in front of a computer in the office, to force myself to use it at home.

I’ve been thinking of RPi and volumio. Mind if I ask few questions.

  1. I’ve heard RPi has some problems with sending hi-res FLAC files. Question is, if I am going to use an external DAC, does this problem still apply? RPi, after all, would be only used to send files through USB; I’d say it should be able of handling that. Any thoughts?
  2. RPi has USB A ports. My DAC has B-type inputs. Will it be possible to connect one to the other?
  1. As far as i know the playback trouble is with higher than CD quality audio.
  2. You would use a USB A - B cable, nothing special about this just the connector form factor. There is no fancy chip or anything in it, this connection is made to make it easier to see what is the host and client side.

Hi. Thanks for a reply.

Ad 1. That’s not good, is it? Sole purpose of having a dedicated DAC is to be able to play music with high density. But does this problem occur if RPi is connected to DAC?


Volumio (and especially MPD it uses) is able to play almost all formats (including Apple lossless, DSD128 and DXD) in bit-perfect fashion with the standard settings. Enabling all kind of mixers (like software volume control, equalizer, re-sampler etc.) forces Volumio to modify the bit stream and thus is not bit-perfect any more.

Biggest ‘challenge’ is when the Digital (bit-perfect) audio stream is Converted to Analog (D/A Conversion = DAC). The quality of the hardware handling this is very much having an effect on the actual listening experience. You can get DAC’s ranging from just a few euro’s to 10K+ euro’s. There is a quality difference in this big range.

Choosing a good DAC (for example an external one as you suggest) is important. My personal experience is that a good (doesn’t mean expensive) external DAC or the ones build-in in some A/V receivers/amplifiers can outperform the ‘simpler’ DAC’s that you connect directly to the RPi.

What remains is the matter of the transport of the digital stream from the RPi to the DAC:

  1. The RPi has a good I2S interface using the GPIO pins. That’s one of the reasons to connect a DAC directly to this I2S interface so there is a short straight through signal path to the actual D/A converters. But again, it is the quality of these D/A Converters that affect the listening experience a lot. (See also some other topics on this forum about the sound quality of these type of DAC’s).

  2. When using an external DAC there needs to be another way of transport.

  • Asynchronous USB seems to be a good option because it allows the DAC to handle the correct timing (Master Clock). But unfortunately the USB bus of the RPi is not its strongest point. It actually only has 1 USB bus (which is used for all four ports like an USB hub AND also for the LAN port, which is actually a LAN2USB device) and it is also an OTG (On The Go) type as well. Connecting a DAC through USB doesn’t always give the desired results due to several (potential) issues with the USB bus. Some people report positive results while others do not.
  • Another option is to get some kind of converter to convert the signal to Coax (Coaxial SPDIF) or Toslink (Optical SPDIF) and feed such a digital signal into the external DAC. Each signal conversion is a potential risk in introducing distortion but this is the trade off, some signal conversion to allow better D/A converters to do the most important conversion. In my opinion a good option is to get a good converter which uses the RPi I2S interface and creates a Coaxial SPDIF signal. Personally I like the sound of my DAC which gets its signal from a Hifiberry Digi+.

Don’t forget to use good quality cables and looking after a good power supply helps also.

Hopefully the above explains the possibilities and some of the pros and cons.

Just downloaded a test file from Linn which is a 24bit 192kHz FLAC Studio Master which played fine

Nice :slight_smile:

What is your setup? And can you post the output of the hw_params (probably /proc/asound/card0/pcm0p/sub0/hw_params) while playing this track?

Well since you said you like to listen to your hundred Cd’s and you CD player is bust I assumed you still want to listen to the same CD’s using volumio.
You would need to RIP the Cd’s, so your music would still be Cd quality audio so it wouldn’t be a problem for you. Besides that, people keep arguing whether or not any one can actually hear the difference. I don’t want to burn my fingers on that discussion and lets not start that here.