OS and Software > All Things Macintosh > [iPhone] Bigger Fail Than Maps ...

reply to Count Zero

Re: [iPhone] Bigger Fail Than Maps ...

while that's theoretically possible - it isn't actually utilized in any real world applications I've seen.

Light travel is theoretically possible -- no one uses it. See the similarity there?

Again, show me a consumer device that actually plays FULL QUALITY audio over bluetooth.

Seriously? I looked through the entire manual to see where it would validate your claim and could not find it (see several posts above). Again - your player uses A2DP and that typically re-compresses audio to 128kbps or less for compatibility. Since ALL of my files are 256kbps AAC or higher then I would expect your player to degrade the quality. Just because BT is theoretically capable of higher data rates DOES NOT mean that they are actually used for consumer applications. You seem to be unable or unwilling to accept that fact.

My ears tell me something different than your perusal of the manual. You can keep arguing but I don't see a point.

EDIT: In fact, the A2DP spec tells me something different than your interpretation of the manual.

See here: »en.wikipedia.org/wiki/Bluetooth_···8A2DP.29

Advanced Audio Distribution Profile (A2DP)

This profile defines how high quality audio (stereo or mono) can be streamed from one device to another over a Bluetooth connection. For example, music can be streamed from a mobile phone, to a wireless headset, hearing aid & cochlear implant streamer, car audio, or from a laptop/desktop to a wireless headset.

A2DP was initially used in conjunction with an intermediate Bluetooth transceiver that connects to a standard audio output jack, encodes the incoming audio to a Bluetooth-friendly format, and sends the signal wirelessly to Bluetooth headphones that decode and play the audio. Bluetooth headphones, especially the more advanced models, often come with a microphone and support for the Headset (HSP), Hands-Free (HFP) and Audio/Video Remote Control (AVRCP) profiles.

A2DP is designed to transfer a uni-directional 2-channel stereo audio stream, like music from an MP3 player, to a headset or car radio.[1] This profile relies on AVDTP and GAVDP. It includes mandatory support for the low-complexity SBC codec (not to be confused with Bluetooth's voice-signal codecs such as CVSDM), and supports optionally: MPEG-1, MPEG-2, MPEG-4, AAC, and ATRAC, and is extensible to support manufacturer-defined codecs, such as apt-X. Some Bluetooth stacks enforce the SCMS-T digital rights management (DRM) scheme. In these cases, it is impossible to connect certain A2DP headphones for high quality audio.

-- Peace.

reply to Count Zero
I think the problem comes down to Apple not supporting MP3 in their A2DP implementation. I suspect that's more popular in bluetooth receivers/speakers than AAC, although they'd all be better off supporting AAC. If the receiving device does not support AAC (which iOS resamples to 132kbps no VBR), then it falls back to SBC - the base compression that all A2DP devices must support, which sounds like shit. All other codecs are optional.

So if your car supports the AAC codec over A2DP, you'll get pretty decent sound quality. 132kbps AAC is roughly equivalent to 256kbps MP3, imo. If it doesn't, you might as well use an FM transmitter hooked up to the audio out.

Source: »developer.apple.com/hardwaredriv···ines.pdf
--
University of Southern California - Fight On!

reply to BronsCon
Nice wikipedia quote. That means IT CAN but does not enforce the support for all of those profiles except SBC (low quality profile).

--PEACE

reply to Thinkdiff
That may well be part of my problem with A2DP but I find very limited information out there about what formats different devices support over BT/A2DP. Also if you have a significant amount of music in ALAC then no BT profile will support the playback of that and it will always be re-converted to something else of lower quality.

I believe you are right about A2DP always re-encoding the audio - regardless of the source - and as well all know going from one lossy format to another will always result in some degradation of audio quality.

I think at the present time that would require the head unit to have a wifi link to your device - though maybe that will change in the future as the newer generations of BT do support higher data rates and there were rumors of future support for AirPlay over bluetooth on Macrumors some time ago as I recall..

reply to Count Zero

Probably, and not at a rate higher than 320kbps - but not a lossless format so any music from your device will require that it be re-encoded for BT and overall disappointing quality/

reply to BronsCon

I understand the difference between playback and transfer codecs and how bluetooth in general works, but thanks for the explanation for anyone who may not.

The example I gave earlier (to which I was still referring) involved an Android phone marketed for its media support and an automotive head unit, so arbitrarily limiting the discussion to AAC at that point really does nothing.

The fact is, a good player will, assuming the playback and transfer codecs are the same, not even bother transcoding and will just send the raw data, which the receiver will decode and play. Since I know my head unit supports WMA, MP3, and PCM as playback and transfer codecs (WMA? really? okay, I'd be less than surprised to find out that nothing else supports that for transfer, because... WHY?!) and I built my music collection out of 320k VBR MP3s based on the fact that my previous head unit supported MP3 but not AAC (via USB or files burned to a CD), coupled with the fact that my phone supports MP3 (possibly PCM, as well, but in this scenario there's no way to tell if it's using it) as a transfer codec, it doesn't matter whether I put the files on a USB stick and plug them into my head unit or stream them over bluetooth, the decoding will be done by the head unit and there will be no loss of quality.

Would I have preferred to use AAC? No, not really, because it's not as widely supported for playback and I don't care how good a codec sounds if I can't hear it. Even my Pioneer head unit, one step down from the top of the line of the current generation, which has full iPhone support doesn't support AAC; it pulls an audio stream, transcoded into a different format (probably MP3) because, as discussed several threads ago, USB doesn't handle analog audio -- so if my head unit doesn't handle AAC, how's it play iPod audio?

Docking isn't always better. Just sayin'.

Our headend supports AAC/MP3/MP4/WMA. All I know is that I can't tell the difference between AAC and MP3 (haven't play WMA files) audio in our car. No one else can either. My guess is that the BT is carrying the data and the HE is decoding, just as you say.
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“The future must not belong to those who slander the prophet of Islam." - Barack Obama, UN Speech 9/25/2012. Ever hear of the First Amendment, BO? Vote Romney/Ryan and take America back.

I have to admit I like the technical discussion going on. But at the end of the day, if the music sounds good for us, that's all we care about. And typically whether we're in the car or at home, we rip at a high enough bitrate that the sound quality is pretty good throughout. I went and did a huge purge of everything that was lower than 256 kbps. Most everything we have now is at 320 kbps. Good enough for us. Again, we're not audiophiles.
--
“The future must not belong to those who slander the prophet of Islam." - Barack Obama, UN Speech 9/25/2012. Ever hear of the First Amendment, BO? Vote Romney/Ryan and take America back.

Now that's what I'm talkin' about!

If I wanted concert quality sound, I'd be recording from virgin vinyl at 24-bit 96khz, to be played back from an SSD installed in a vehicle-mounted PC connected directly to a pair of $5k 2Kw digital amps powering an array of speakers costing no less than $20k.

But, since I just want to enjoy my music without having to fiddle with cables or spend 3mo salary, Bluetooth works great.