What are head-fi members views on apt-x lossless codec (over bluetooth)?

[davidmthekidd]

BT-aptX isn't lossless, but it sounds better to my ears than the usual BT-SBC encoding. As far as I know, there's no BT-AAC and your AAC files will be re-encoded to SBC for BT streaming.

That said, according to this comparison, even good old SBC has very good audio quality at 320kbps, with artifacts below hearing threshold.


There seem to be very few aptX adopters here on head-fi, however the list of aptX compatible devices has been steadily growing ever since the start of this thread.

As I said above, BT streaming will always involve lossy re-encoding, regardless of whether SBC or aptX is used. From my point of view the question is, will you be able to hear the difference? Try opening a JPEG file in your photo editor and save it to a new file at 95% JPEG quality. The second file will obviously be a lossy degradation of the first one, but good luck on trying to discern the visual differences. (Of course, things will look different if you save the new file at 75% or lower).

Perfect analogy.

 

[watchnerd]

aptX just doesn't fit my use case (so far).
 
I don't walk around my house and play stuff from my phone.  And I already have lossless streaming set up over AirPlay.
 
aptX for my car might be cool, though.

 

[Giogio]

Perfect analogy.

But wrong. AAC is not only a compression format but also a BT audio Codec, the only alternative to SBC in iOS devices till now.

 

[Giogio]

  aptX just doesn't fit my use case (so far).
 
I don't walk around my house and play stuff from my phone.  And I already have lossless streaming set up over AirPlay.
 
aptX for my car might be cool, though.

Well, you can still walk around your house and play stuff from your Mac, and use a BT headphone, and APTX, for that.
OSX supports Aptx natively.
I only use headphones lately, no speakers. Because I moved a lot in the last years.
And the freedom of BT headphones is a bliss. Never EVER again wires for me.
 
Now, if there were AirPlay headphones, this would be nice.
I suppose it is not possible or people would have done this already, at least, wifi headphones...

 

[watchnerd]

 
Well, you can still walk around your house and play stuff from your Mac, and use a BT headphone, and APTX, for that.
OSX supports Aptx natively.
I only use headphones lately, no speakers. Because I moved a lot in the last years.
And the freedom of BT headphones is a bliss. Never EVER again wires for me.
 
Now, if there were AirPlay headphones, this would be nice.
I suppose it is not possible or people would have done this already, at least, wifi headphones...

 
When I have speakers in 3 different rooms, I don't really have a reason to do that.

 

[Giogio]

   
When I have speakers in 3 different rooms, I don't really have a reason to do that.

Then you either have very nice and permissive neighbours, or no neighbours at all, and nobody else living with you, or you do not like to listen to music at loud volume late at night.

 

[watchnerd]

  Then you either have very nice and permissive neighbours, or no neighbours at all, and nobody else living with you, or you do not like to listen to music at loud volume late at night.

 
I own my own house, neighbors are far enough away, and I do have a wife who indulges my listening habits.

 

[Giogio]

   
I own my own house, neighbors are far enough away, and I do have a wife who indulges my listening habits.

The day I find the right woman I wish she will indulge my listening to Dubstep or Techno at max vol at 3 in the night.
That would be my twin soul.
Happy that you found one

 

[watchnerd]

  The day I find the right woman I wish she will indulge my listening to Dubstep or Techno at max vol at 3 in the night.
That would be my twin soul.
Happy that you found one

 
Oh, 3 am? No...I've got a job.
 
Listening usually ends around midnight.

 

[Giogio]

   
Oh, 3 am? No...I've got a job.
 
Listening usually ends around midnight.

Oh, yeah, me too, but I do not work on weekends, and have long forced pauses from time to time when weather is not good, so I find myself enjoying night often, which I like, as my natural rhythm is being awake at night.
And even when I have to work I do not start too early in the morning, I must leave home at 7:45, so I can even wakeup 7:30 if I was too late the night before. Which is usually not 3, but can be after midnight. As said, I like night.
 
Anyway, we are going off topic.
Enjoy your speakers

 

[james444]

  But wrong. AAC is not only a compression format but also a BT audio Codec, the only alternative to SBC in iOS devices till now.

 

• Don't think I've been wrong when I posted that in 2013. Afaik there weren't any BT chips available that supported AAC back then.
• Read this post. A2DP is a packet oriented protocol. I'm pretty sure that even AAC to BT-AAC involves re-encoding.

 

[Giogio]

   

• Don't think I've been wrong when I posted that in 2013. Afaik there weren't any BT chips available that supported AAC back then.
• Read this post. A2DP is a packet oriented protocol. I'm pretty sure that even AAC to BT-AAC involves re-encoding.

Oh, did not see it was an old post. The quoter did a lot of reading apparently.
I did not say anything about not re-encoding. I was involved in that conversation as you see. So I remember that. But I still wish to have other opinions about it. I can't believe it is like that.
It is just a useless extra passage, it adds latency, it may degrade the sound, it is pointless.

 

[james444]

  Oh, did not see it was an old post. The quoter did a lot of reading apparently.
I did not say anything about not re-encoding. I was involved in that conversation as you see. So I remember that. But I still wish to have other opinions about it. I can't believe it is like that.
It is just a useless extra passage, it adds latency, it may degrade the sound, it is pointless.

 
Bluetooth uses adaptive frequency hopping to avoid device interference and ensure that transmission works well, even in crowded environments. BT-audio transmission is a continuous stream of small packets being concurrently sent over multiple frequencies. The chopping of audio at the source and reassembling at the sink is anything but pointless, it's in fact absolutely essential to ensure a robust transmission. If there existed a fast and efficient method to chop audio (particularly vbr) into packets without re-encoding, now that would be great, but afaik there is none.

 

[Giogio]

   
Bluetooth uses adaptive frequency hopping to avoid device interference and ensure that transmission works well, even in crowded environments. BT-audio transmission is a continuous stream of small packets being concurrently sent over multiple frequencies. The chopping of audio at the source and reassembling at the sink is anything but pointless, it's in fact absolutely essential to ensure a robust transmission. If there existed a fast and efficient method to chop audio (particularly vbr) into packets without re-encoding, now that would be great, but afaik there is none.

Well, Aptx does re-encoding anyway. And AAC too, when not playing an AAC file. So what I do not understand is why should all files be converted to pcm before being converted to aptx or aac. Specially when playing AAC files in AAC codec, which would give the possibility to transmit directly to AAC (given that it is the codec used, so it should not be needed any other "conversion". Otherwise what are codecs for?).

 

[james444]

  Well, Aptx does re-encoding anyway. And AAC too, when not playing an AAC file. So what I do not understand is why should all files be converted to pcm before being converted to aptx or aac. Specially when playing AAC files in AAC codec, which would give the possibility to transmit directly to AAC (given that it is the codec used, so it should not be needed any other "conversion". Otherwise what are codecs for?).

 
@ClieOS already posted a perfect explanation. Really not much to add, except that you need constant bitrate to efficiently chop audio into packets, which is another reason for PCM as an intermediate format.
 

   
Regardless of what file format you use, it will always get decoded to PCM first. Formats like mp3, AAC, FLAC or ALAC is just a container, they defines how files is stored in a particular way, but they doesn't tell what kind of data is inside. That data is PCM. So basically we have one way of saving PCM called mp3, another way called AAC, another called FLAC, etc. When these files (mp3 / AAC / FLAC / etc) are played, the computer 'restored' it back to the purest form first, which is PCM, then it is fed to the DAC (or the BT chip for further re-encoding for transmission).
 
Taking your example:
AAC files played -> convert to PCM -> send to BT chip -> re-encoded to aptX -> send the aptX to receiver -> receiver take the aptX and convert it to PCM -> fed to DAC and becomes analog sound.
 
(*the red part can be SBC or AAC, depends on what is supported on both transmitter and receiver)
 
If you think it is a pity that AAC get converted to PCM, then you have the wrong idea. PCM is one of the two most basic form of digital audio data (the other one is DSD). But PCM is too big to store, so we process it with codec like mp3 or AAC in order to compress it down to the file size (and quality) that we can live with. So converting AAC to PCM is basic a process of restoration. It is equal to unzipping a file to reveal the original data. If you don't ever want to unzip a file, how would you have any access to the data inside? Therefore the process is a MUST.