[Venasa]

I've been thinking about signal flow for bluetooth headphones recently and have come to the following conclusion. An external DAC and/or amp are superfluous when listening to music through bluetooth headphones because the headphones necessarily have their own DAC and amp. Any SQ benefits gained earlier in the signal flow would be negated by the bluetooth headphones DAC and amp which necessarily sit right before the headphone speakers. The only way to improve bluetooth audio SQ is a better transmission codec (aptxHD etc), better source file fidelity, and of course better bluetooth headphones.

Is that all correct? and why?

 

[redrol]

yes that is correct, pretty much only LDAC is acceptably transparent, so use that

 

[bigshot]

I get fine sound quality from bluetooth on my iPhone without a separate DAC or amp. I use AAC and that is transparent.

 

[Roseval]

Is that all correct? and why?

The "why" is simple.
Assuming a digital source (an analog source must be digitized before it can be send over BT);
the audio is send to a BT transmitter. There it is compressed using the codec negotiated between sender and receiver.
At the receiver it is decoded and send to a DAC to be converted to analog and amplified to drive the drivers.

Using external DACs or amps indeed won't help you as you are adding a redundant analog stage.
Better stay in the digital domain.
In the past BT audio often sounded horrible. To save bandwidth a small bit pool was used.
Today even SBC sounds good when using a bit pool of sufficient size.

A bit more about codecs: https://habr.com/en/post/456182/

 

[redrol]

I get fine sound quality from bluetooth on my iPhone without a separate DAC or amp. I use AAC and that is transparent.

I'll take LDAC thanks.

 

[bigshot]

SBC isn't the same as AAC. I've found a little rolloff at AAC 192, about the same as that chart, but by 256 it seems to be full range, and VBR would only allow more headroom for high frequencies. (EDIT: I googled the answer and updated this post below.)

Although it's not like there is a lot of musical content that high... Above 15kHz is less than two whole notes on the musical scale, and it's at the bleeding edge of human hearing for most people. They did a study where they rolled off everything above 10kHz, compared it to 20-20 and asked if the subjects could hear 1) a difference and 2) a preference for which one had the best sound quality. Some listeners indicated that they could hear a difference between rolled off and full range, but there was no indication that either one sounded better to them than the other. Of course, it's best to have all the frequencies, but for the kind of portable use bluetooth is designed for, you aren't going to hear that high anyway. If you want that kind of critical listening you should plug in and listen to lossless.

EDIT: I googled this and found out what the problem is. AAC requires more processing power than the other codecs, and the way Android's EAC (Energy Aware Scheduling) is set up, if you have battery saver turned on, it may not assign enough of the processor to properly render AAC files. It varies from phone to phone. Some are like the chart you have there rolling off at 14kHz, other Android phones go up to 17kHz. Apple phones have more processor assigned to sound, so they go up to 19kHz and roll off with a much less drastic attenuation. It's the same with noise levels. Android phones are all over the place, and Apple phones are stone silent. The AAC codec is capable of audible transparency, but if you have a cheap Android phone, you aren't going to hear everything that is in the file. It isn't AAC's fault. It's the phone. aptX is best for Android. AAC is best for Apple phones.

 

[HipHopScribe]

I'll take LDAC thanks.

Ha, as if I can still hear up to 15 kHz.

Seriously though, with most music going into most ears, that audio above 15 kHz probably doesn't actually matter

 

[bigshot]

And even if you can hear 15kHz, that only exists in recorded music in cymbal crashes, which contain enough lower octaves to completely mask any of the stuff above 15kHz.

I won't argue that it isn't good to have frequencies above 15kHz. But you're right, it probably doesn't make a lick of difference. And both aptX and AAC have pretty much identical specs, depending on whether you are using Android or iPhone. So it probably isn't work worrying about. Just use whatever the default is for your phone and you will be fine.

 

[redrol]

Sure all that is right, but hey I have LDAC (most Androids have it) and use it constantly. No downsides and I get pretty well full fidelity.

 

[bigshot]

I doubt there’s much of an audible difference between codecs. I really don’t think people need to worry about Bluetooth any more. It pretty much just works with whatever defaults you have. Back when it was first introduced, it could be funky and the sound quality was just OK. But now I don’t think about it any more and it just works. I haven’t used my wired cans in quite a while.

And in answer to the OP’s question, I don’t think there is any point to DACs and amps at all unless you want to use some kind of specific cans or IEMs that require them. I have fantastic sounding headphones that I can plug straight into my iMac and they sound as good as with a fancy DAC/amp. And I have really good sounding AirPods that sound great over Bluetooth for portable. I’d rather carry my phone and AirPods in my pocket than haul around a bunch of black boxes and cables in a backpack.

 

[redrol]

See, I just use a 80 bux Radsone ES100 portable tiny amp and my LG phone. It's hard to complain, cheap, effective and sounds great.

 

[bigshot]

I just carry an iPhone and a little AirPods Pro case.

 

[redrol]

I've killed too many phone jacks and cables, the es100 at least lets me separate the cable from my phone. Also I actually need 10 hours of battery life for trail running.

 

[bigshot]

My rig can do that wireless on battery… not uninterrupted, but I can’t run for ten hours uninterrupted. I can’t even run ten minutes!