Reply To: DTS Pass through

21. Oktober 2015 at 13:00 #16463

Hi Maximillian

So sorry if I was not clear. I was not talking about losing quality with hi-res flac. I have hi-res audio enabled over HDMI and it works perfectly!

This is what I mean by DTS passthrough.

It is possible to embed a 5.1 DTS stream in a flac wrapper (not limited to 5.1), which LMS and squeezebox see as a „normal“ flac file. A Squeezebox connected to a surround amplifier via coax or s/pdif will pass this file unconverted to the surround amplifer provided the Squeezebox is in passthrough mode, which is enabled by setting the output volume to be fixed at 100%. The amplifier identifies the DTS (or AC3) stream and handles it accordingly. This is a very cool feature of Squeezebox that is relatively unknown but allows those of us who have surround sound mixes of treasured albums to add these to our Squeezebox library and play them like any other album.

The DTS files can be ripped from the „video“ part of any DVD-Audio or audio bluray (or created from the lossless multichannel these discs may also have if you have expensive DTS conversion software). I have many such files (e.g the King Crimson 40th Anniversary Series, etc.) which play perfectly in 5.1 DTS using a Squeezebox Touch.

The embedding is done using a python script. As the link below states: „ is a Python script which takes as input an AC3 or DTS file (sourced from a DVD) and encapsulates it in an IEC61937 stream. This stream is then wrapped in a WAV file which can be played over an S/PDIF link with no modifications (ie no volume adjustments); a digital receiver will be able to interpret the AC3 or DTS data contained within this stream (assuming the receiver knows the AC3/DTS formats).“

The script works perfectly to produce a WAV file with DTS embedded in it. You can then convert this WAV file to flac using flac.exe in the normal way, which does not actually compress the file further but the flac wrapper allows you to add the meta data to the file to catalog it with LMS as you would any other music file.

More details are given here:

Your implementation of squeezelite in max2play (I have v2.23) must modify the stream in some way, because these DTS-encoded files just produce „white“ noise over HDMI. Although I do not understand the finer technicalities I believe the key is that the player passes the stream to the amplifer completely unmodified.

I know that passthrough of these files over HDMI is possible with Squeezelite, because this works on picorep***er up to v 1.18b (sorry to keep referring to an inferior rival!), but the writers of that software seem to have broken the function since then and do not seem to be interested in answering my question as to whether they intend to fix it. I think the code is available at sourceforge. Max2Play is much cooler and more versatile and it would be great if it added this function.

I hope this helps. I can provide you with an example DTS-encoded flac file if that would help.

Best regards


ps If you want to get the hang of these DTS-flac files, foobar can deal with them perfectly happily. With the DTS component enabled foobar identifies the DTS stream in the flac file and converts it on the PC. But if you want to use the higher quality conversion of your surround amp you can perform a similar trick of passing the DTS direct to the amp by simply removing the foobar DTS component. In this case you will get „white“ noise if you try and play the file direct to speakers attached to the PC but if your PC is attached to a surround amp via HDMI then foobar does not attempt to read the file but simply sends the flac file to the amp unaltered.

  • This reply was modified 5 years, 1 month ago by  d4n3ll.