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Strange Behavior in Playing Back Audio Files

Here's something I just can't figure out. It won't diagnose.

I have lots of audio files, mixed mp3, AAC, etc. on an AK70 Mark II player. I listen to them through B&O H5 bluetooth earphones, and for the most part, all seems fine. Now here comes the problem:

Although most of the many thousands of audio files play back fine, a lot of them consistently play back distorted. Any file that plays back fine ALWAYS plays back fine. Any file that plays back distorted ALWAYS plays back distorted. So, for any given time I am connected, I can always play back some files always fine, and the ones that are bad are always playing back distorted.

So, I think, it can't be a bad bluetooth connection. So, maybe the original files that are playing back badly are themselves in bad shape? So I go to the source, the internal hard drive of the computer, and from the computer speakers, they play back fine.

Next, while unlikely, I think that maybe all of these files, and not the good files,  copied over badly? But no. When I listen to the files on the player using a headphone directly connected to the player, these bad file always sound fine. But when I try then to listen to them over bluetooth, these files (AND NOT THE "GOOD" FILES) are again always playing back badly.

So it's not the files (since both good and bad files play back fine when listened through a direct headphone connection) , it's not the player (since it is playing them both back fine when listened back through a direct headphone connection), it's not the bluetooth connection with the earphones (since the good files play back fine, and only the bad ones play back badly), and it's not the earphones (since they are always playing back good files properly, and besides, I get the same behavior when I do a bluetooth conenction with a UE Boom 2).

I give up. What could it be?

Re: Strange Behavior in Playing Back Audio Files

Reply #1
Sounds like a firmware bug.

Re: Strange Behavior in Playing Back Audio Files

Reply #2
A firmware bug of the player? How could that affect only certain files and only when just those files are played through bluetooth?

Re: Strange Behavior in Playing Back Audio Files

Reply #3
You didn't describe the type of distortion, and you didn't identify any characteristic in the bad sounding files (although there might not be a common one).

I found the following reference manuals from your equipment (which I've used to get an Idea of your problem):
https://www.beoplay.com/~/media/manualspdf/beoplay-h5/3511439_1606_beoplay_h5_a_online_web.pdf?la=en
http://www.iriver.com/download/download.asp?dNum=1155&dfNum=2873

The wireless earphones indicate that they use bluetooth 4.2 and aac codecs (On their web. the manual doesn't include technical information). They come only with the earphones, different tips and clips, and a charger.

While one selling point of the player is their DACs, I found in the manual that indeed, it has bluetooth connectivity. It describes it as supporting:
Quote
Profile: A2DP,  AVRCP, aptX, aptxHD
 Device performance may be affected during Hi-Fi playback.
 (48 kHz or lower is recommended.)

So, with this, it is to be expected that the audio is transmitted using the standard A2DP bluetooth codec.

I cannot discard that the problem be caused by "killer samples" for the codec (It is to be expected that it uses a high bitrate, but I don't know), and maybe the problem is affected by the loudness of the files (I didn't find any mention to replaygain or any loudness control, so I assume that it does not have such thing).

Since it supports different codecs, it might be possible that with other bluetooth devices it does not fail, but this is complete speculation.
Also, for some reason, it says that it does not support Car Audio bluetooth, (Which I don't understand. If it is mean generally as bluetooth used in car players, I can't understand why one would add such a limitation.  I've been using my old smartphone with my new Toyota's bluetooth audio and the only fault is the smartphone not supporting a high enough standard of the control protocol, so I cant' search or seek, only skip to next/previous).

Re: Strange Behavior in Playing Back Audio Files

Reply #4
Thank you. I'll review your response. Thanks for taking the time to think about it. Note I indicated that this did not just occur when played through the H5, but also through UE Boom 2 Bluetooth speakers.

Here's further information. The type of distortion is always exactly the same for each bad file. One can just recognize the song. I have attached a short sample of one file, as recorded on my iPhone played via Bluetooth through the UE Boom 2 speaker.

[Further...] I reviewed your response. It seems unlikely that all of these files would have been created using some kind of "killer" codec that only happens when playing via Bluetooth, while other files of similar ilk are not affected, no?

Re: Strange Behavior in Playing Back Audio Files

Reply #5
My guess is that something strange is in the header of the file, which prevents it to be decoded right. Can you remove ALL metadata from the file and play it back like that? No pictures, no lyrics, no tags of any kind.

Re: Strange Behavior in Playing Back Audio Files

Reply #6
My guess is that something strange is in the header of the file, which prevents it to be decoded right. Can you remove ALL metadata from the file and play it back like that? No pictures, no lyrics, no tags of any kind.

I can try that, but if you are right, it doesn't account for the fact that these "bad" files play back perfectly fine on my computer through speakers, and fine through the player as long as it is not going through Bluetooth.

About the only thing I haven't tried is getting a cheap Bluetooth transmitter, and seeing if it plays fine when connected via Bluetooth through the headphone jack of the computer speakers.

But this is crazy...

Re: Strange Behavior in Playing Back Audio Files

Reply #7
 
A firmware bug of the player? How could that affect only certain files and only when just those files are played through bluetooth?

Yes the players firmware. Random compatibility problems are common on these niche players.

Re: Strange Behavior in Playing Back Audio Files

Reply #8
After looking at the file with Audacity, what I can see is that it has periodical skips in the audio (not fully silence, but quite obvious with the drums. Also, since this is analog recording, it might have more distortion coming from playback).

Given that it is so periodical, I am with saratoga, that this is probably a bug in the player, or more specifically, some limits or values that these files produce that the firmware didn't expect.
You can try finding if playing back from a different bluetooth emitter works, but so far, it seems that you will need to contact with the manufacturer.


Re: Strange Behavior in Playing Back Audio Files

Reply #9
After looking at the file with Audacity, what I can see is that it has periodical skips in the audio (not fully silence, but quite obvious with the drums. Also, since this is analog recording, it might have more distortion coming from playback).

Given that it is so periodical, I am with saratoga, that this is probably a bug in the player, or more specifically, some limits or values that these files produce that the firmware didn't expect.
You can try finding if playing back from a different bluetooth emitter works, but so far, it seems that you will need to contact with the manufacturer.

Thanks.

But why would it have picked THESE particular several dozen (or many more) files to have problems with, but not many others?

It seems like this could not be a player type issue, but a file-related issue. And why only with Bluetooth. I remain puzzled.

Re: Strange Behavior in Playing Back Audio Files

Reply #10
And now, we have an even more ridiculous situation.

For one song, I have the earphones connected with Bluetooth (AptX) and I insert and remove regular headphones. When its only the earphones, I get the distorted sound. When I insert the headphones, it plays fine, picking up where it left off at.

For a "good" song, it plays fine with either one.

Excuse me while I go pull my hair out (whichever hairs are left)

Re: Strange Behavior in Playing Back Audio Files

Reply #11
Return the player and get one with better Bluetooth support.

Re: Strange Behavior in Playing Back Audio Files

Reply #12
An answer:

I tried this microSD card with the songs in a few other audio players. A model 1 AK70 showed the same behavior. However, an earlier AK JR did NOT. With the last one, it played that same darn song "Sugar Shack" fine even with Bluetooth. hm....

Then I realized that most of the problem songs were mid-60's, or earlier. For example, my 1964 directory was *mostly* problematic. Hm.....

I then tried doing an analysis of directories (I have them by year) with Similarity. I noticed that virtually all of the songs in my 1964 directory were MONO. Hm.... I then tried the songs that were stereo. They all played fine in bluetooth, even though they were in the 1964 directory. But all the MONO songs were problematic.

So, I have sort of solved the problem, even though it does not make sense. Why should a MONO song play fine via headphone for these players, but not in Bluetooth? The AK70 Mk2 does have the latest Bluetooth, and APTx, and now I guess I have to contact hte manufacturer.

 
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