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  1. #1
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    24-bit ALAC files being truncated to 16-bit?

    Hi folks,

    Apologies in advance if this has been answered - did a couple of searches but came up with nothing conclusive.

    I'm running LMS 7.7.3 (last official release), streaming ALAC files from my Mac to my SB Touch. Works great - except I just discovered this strange issue.

    In the LMS web interface, most - but, strangely, not all - 24-bit files are showing up as 16-bit instead. And they are showing up that way not only while streaming, but even when they're not playing.

    I have not recently updated LMS or changed the SB Touch's firmware. But unfortunately I am not 100% sure it didn't always do this, since I haven't viewed the LMS Info window very often until recently.

    The only files I've found so far that show up as 24-bit in LMS are files that use a 48kHz sampling rate. However, the files that show up as 16-bit include 48kHz ones (as well as 88.2 and 96khz ones).

    The files show up properly as 24-bit in iTunes, and as far as I know they play through iTunes locally at 24-bit resolution (I have my Mac's audio output set to 24/96 in Audio MIDI setup - I realize this does not apply when streaming via Airplay; I am talking about the output at the Mac's optical/analog-out jack).

    My questions:

    (1) Is this just a glitch in the Info display, or is LMS really truncating most of my 24-bit ALAC files to 16-bit?

    (2) Since the files show as 16-bit in the Info window even when they're not currently playing - in some cases, when I've never played them through LMS - doesn't that mean the issue is occurring during scanning of my library, rather than during actual streaming?

    (3) If it's really truncating my files, does anyone have an idea why? I am willing to upgrade to LMS 7.8 (or 7.8.1?) if people think that will help - but I don't want to upgrade unless there's a reason.

    Thanks for any info or insight folks can provide.

    Best,
    Matt
    Last edited by tmtomh; 2014-08-30 at 19:04.

  2. #2
    Senior Member Mnyb's Avatar
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    What info ? if you play to a player that needs transcoding the bitrate info gets bogus , but the sample rate and sample size info is read from the files themselves .
    See this picture .
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  3. #3
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    Quote Originally Posted by Mnyb View Post
    What info ? if you play to a player that needs transcoding the bitrate info gets bogus , but the sample rate and sample size info is read from the files themselves .
    See this picture .
    Thanks for your quick reply. The Info I'm referring to is the Sample Size. Here are two screenshots.

    (1) A 24-bit, 192kHz file that is currently streaming/playing. Because the SB Touch only supports 96kHz sample rate (yes?), this file includes the "converted to 705kbps FLAC" info under "bitrate," which you highlighted in your screenshot:

    Name:  15088634222_034ca65b66_c.jpg
Views: 555
Size:  89.5 KB

    (2) A 24-bit, 96kHz file that is NOT currently streaming/playing. This file does not need to be transcoded:

    Name:  15088991605_883468e177_c.jpg
Views: 551
Size:  88.7 KB

    Note that in both screenshots, it says "Sample Size: 16Bits". This is not correct - these are 24-bit files. My question is, is this (A) a display bug; or (B) is LMS incorrectly seeing these files as 16-bit when it scans my library - and is it therefore streaming them to the SB Touch using only 16-bit bit depth instead of the proper 24?

    The files do show the correct sample rate, bitrate (5504kbps on the first one, 3173kbps on the second one), and file size - only the bit depth is wrong.

    Also, I just cleared and re-scanned my entire iTunes library with LMS, and the problem persists.

    Thanks for any insights or help folks can provide.
    Attached Images Attached Images   
    Last edited by tmtomh; 2014-08-30 at 19:59.

  4. #4
    Senior Member Mnyb's Avatar
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    I actually don’t know ?

    and this is happening with some alac but not all ?

    To see what transcoding parameters is picked you could go to settings/advanced/logging and select log set transcoding .
    And then select a track and play it and then study the server.log .
    ALAC will be transcoded as most squeezeboxes dont do alac natively and Touch's native decoder dont do hirez

    It could be a scanner bug in that it only the presentation thats wrong .
    BTW a squeezebox is always sending 24bit even with 16bit material.

    Do you use the iTunes integration or are letting LMS scan the iTunes music folder directly ?

    Is there any difference in how you ripped or decoded those files .

    If you want to report a bug go here ,but be prepared to provide a sample file (you use a link to dropbox or some similar service ) , if its a scanner error it can be something about your files it does not like and it may not be a general problem

    http://bugs.slimdevices.com/
    --------------------------------------------------------------------
    Main hifi: Rasbery PI digi+ MeridianG68J MeridianHD621 MeridianG98DH 2 x MeridianDSP5200 MeridianDSP5200HC 2 xMeridianDSP3100 +Rel Stadium 3 sub.
    Bedroom/Office: Boom
    Loggia: Raspi hifiberry dac + Adams
    Bathroom : Radio (with battery)
    iPad with iPengHD & SqueezePad
    (spares Touch, SB3, reciever ,controller )
    server Intel NUC Esxi VM Linux mint 18 LMS 7.9.2

    http://people.xiph.org/~xiphmont/demo/neil-young.html

  5. #5
    Senior Member Mnyb's Avatar
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    My only test file present itself as 24bit 96kHz and use dBpower amp to create that one I dont have enough alac files to test further .
    --------------------------------------------------------------------
    Main hifi: Rasbery PI digi+ MeridianG68J MeridianHD621 MeridianG98DH 2 x MeridianDSP5200 MeridianDSP5200HC 2 xMeridianDSP3100 +Rel Stadium 3 sub.
    Bedroom/Office: Boom
    Loggia: Raspi hifiberry dac + Adams
    Bathroom : Radio (with battery)
    iPad with iPengHD & SqueezePad
    (spares Touch, SB3, reciever ,controller )
    server Intel NUC Esxi VM Linux mint 18 LMS 7.9.2

    http://people.xiph.org/~xiphmont/demo/neil-young.html

  6. #6
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    Think I Found the Answer

    Thanks for the input and helpful replies. I think I found the source of the problem, and it's a weird one: I discovered that every high-res file LMS showed with the proper 24-bit sample size had been encoded by XLD. And every one it showed as 16-bit had been encoded by Max.

    Max is an older program created by the same person who makes XLD (both apps are Mac-only as far as I know). Max is no longer being updated and in many ways XLD is more capable. But Max has a much more convenient interface than XLD when it comes to batch-tagging digital files before transcoding them, so I usually use Max. (For some reason, XLD won't let you batch-tag files except when you rip them from a CD.)

    Every other app - iTunes, Foobar2000 in Windows, and others - sees Max-encoded high-res files properly as 24-bit. And over the years when I've had occasion to load Max-encoded high-res files into an audio editor, there's been musical information beyond 22.05kHz, so I know Max is indeed producing the proper high-res files. So my guess is that Max is failing to include something in the metadata for the file that LMS needs in order to see it as a high-res file.

    I was going to re-encode all my original FLACs to ALAC using XLD, but I discovered that I could fix the problem slightly more easily by simply running my Max-created ALAC files through XLD - "transcoding" ALAC to ALAC. The resulting files are bit-identical, retain all the metadata I added during the original FLAC-to-ALAC conversion, and properly show up as 24-bit in LMS. The only drag is that I have to manually re-rate them and copy over the album art in iTunes. And of course I have to add all the new files and delete all the old ones. I am about 1/3 of the way through.

    Ideally I would love to be able to load a Max-encoded ALAC into an extended metadata app and find the missing bit, so I could just modify the metadata and not have to re-transcode everything. Any ideas?
    Last edited by tmtomh; 2014-08-31 at 07:19.

  7. #7
    Quote Originally Posted by tmtomh View Post
    Thanks for the input and helpful replies. I think I found the source of the problem, and it's a weird one: I discovered that every high-res file LMS showed with the proper 24-bit sample size had been encoded by XLD. And every one it showed as 16-bit had been encoded by Max.

    Max is an older program created by the same person who makes XLD (both apps are Mac-only as far as I know). Max is no longer being updated and in many ways XLD is more capable. But Max has a much more convenient interface than XLD when it comes to batch-tagging digital files before transcoding them, so I usually use Max. (For some reason, XLD won't let you batch-tag files except when you rip them from a CD.)

    Every other app - iTunes, Foobar2000 in Windows, and others - sees Max-encoded high-res files properly as 24-bit. And over the years when I've had occasion to load Max-encoded high-res files into an audio editor, there's been musical information beyond 22.05kHz, so I know Max is indeed producing the proper high-res files. So my guess is that Max is failing to include something in the metadata for the file that LMS needs in order to see it as a high-res file.

    I was going to re-encode all my original FLACs to ALAC using XLD, but I discovered that I could fix the problem slightly more easily by simply running my Max-created ALAC files through XLD - "transcoding" ALAC to ALAC. The resulting files are bit-identical, retain all the metadata I added during the original FLAC-to-ALAC conversion, and properly show up as 24-bit in LMS. The only drag is that I have to manually re-rate them and copy over the album art in iTunes. And of course I have to add all the new files and delete all the old ones. I am about 1/3 of the way through.

    Ideally I would love to be able to load a Max-encoded ALAC into an extended metadata app and find the missing bit, so I could just modify the metadata and not have to re-transcode everything. Any ideas?
    Sorry to revive an old thread, but I'm having nearly exactly the same issue. The only difference for me is that the problem encoder is ffmpeg. I am wondering if max uses ffmpeg under the hood to do the encoding?

    I have a group of 24bit files that were converted from flac to alac using ffmpeg. Other players such as iTunes, JRiver Media Centre and Kodi report them as being 24bit. 24bit files encoded using other software are reported correctly as being 24bit in LMS.

    I've just re-encoded one of those albums using JRiver (alac-alac) and rescanned the library. That album is now showing as 24bit.

    I'm not sure that this necessarily causes any playback issues except when using the UPnP/DLNA bridge. Playing these files through the bridge produces static only.

    This is feeling like a bug in the scanner. Anybody got any thoughts?

    Is it time to report it?

    Thanks.

  8. #8
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    Quote Originally Posted by pssturges View Post
    Is it time to report it?
    LMS is now community suipported so unless it is clearly an LMS and not a bridge problem, it may not get attention.

    To prove it is not a bridge problem, have you tested using something with a h/w SB player or Squeezelite on a PC ?

  9. #9
    Quote Originally Posted by bpa View Post
    LMS is now community suipported so unless it is clearly an LMS and not a bridge problem, it may not get attention.

    To prove it is not a bridge problem, have you tested using something with a h/w SB player or Squeezelite on a PC ?
    Well, I guess there is 2 parts to the issue.

    1) LMS does seem to scan the files incorrectly and report the wrong properties. This seems clearly to be an issue with LMS

    2) The second part is what effect does this have on playback? I've tried playing them through squeezlite and they "seem" to play OK. Whether or not they are playing correctly and efficiently I can't say. Also, whether or not the bridge is at fault, I'm sure it would be helpful if it was receiving the correct information about the file from LMS.

    I'd be happy to do further testing to try and isolate the issue.

    Thanks

  10. #10
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    Quote Originally Posted by pssturges View Post
    1) LMS does seem to scan the files incorrectly and report the wrong properties. This seems clearly to be an issue with LMS
    Start with the first item.

    To understand what is really going wrong is it the scanning or the transcoding ? - provide the debug output of the scanner.log file for this problem file and then the server.log with player.source set at INFO when playing this file to a SB player / Squeezelite.

    If the file plays OK through SB players and Squeezelite - then the issue is with the matching of player capabilities as reported by the bridge plugin and the detailedinfo about the file.

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