Apple iPhone OS 3.0 shines fresh light (and enmity) on A2DP Stereo Bluetooth

So it's clear from my Google Analytics data that since the release of iPhone OS 3.0, there is a heightened interest in Bluetooth stereo audio. There is also concern about its quality, and whether it sounds like shit on purpose.

Well let me tell you, something funky is definitely going on with the Bluetooth stereo audio performance on the iPhone. Your suspicions are not unwarranted. The bottom line is that Bluetooth A2DP as implemented in the iPhone will sound like shit. Anyone with an ear (but not a preference) for audio distortion will corroborate there is a ton of it when listening to Bluetooth wireless audio on the iPhone running 3.0 OS. High frequency sounds such as symbal-hits sound like digital-ringy-thrash-crap. Awful. Un-listenable. Period.

After poking around a bit, it seems (I suspect) Apple may be short-changing users on the bitpool allocation. From an internet discussion regarding hacking BT performace via Windows registry, it is noted that the Bluetooth A2DP implementation guide outlines how to adjust over-the-air quality for A2DP:

Medium Quality
BitPool=35, SampleRate=44.1khz = 229kb/s
BitPool=33, SampleRate=48khz = 237kb/s
High Quality
BitPool=53, SampleRate=44.1khz = 328kb/s
BitPool=51, SampleRate=48khz = 345kb/s

The trade-off is of course weighed and excuted by Apple. It appears, and logic would backup, that the source device in the A2DP link is the "decider" for the bitpool. The setting, that is, that determines bitpool is embedded in the iPhone itself, rather than the receiving BT accessory.

All bitrates are not created equally

Do NOT be fooled. The bitrates you see above are not typical compression bitrates you are used to seeing in your desktop music libraries. BT doesn't use a fancy psychoacoustic lossy compression scheme like MP3 or AAC (optional A2DP codecs, btw, but neither employed by Apple). The standard for A2DP Bluetooth uses sub-band coding (SBC) for compression. SBC is royalty-free, low complexity, low latency, and by many measures, a crude form of compression. The bitrates that apply to it do not yield the same sound quality at comparable bitrates of MP3 or AAC. Some estimates are that you require 3x the bitrate to achieve comparable quality to MP3. To highlight just how much better MP3 and AAC are consider, AAC and MP3 are not royalty free, and in spite of that, they are employed in infinitely more places, and are thus commercially acceptable. You get what you pay for, people.

Doubling down on lossy

Also keep in mind that you are *re-compressing* an audio file that has already been uncompressed from a lossy codec (MP3 or AAC). Meaning, the original CD-quality track (1411 kbps) was compressed using some (better) codec like MP3 or AAC. Do it once and the quality is very acceptable for most consumers at 192 kbps or above, even if it is mildly, and unarguably, degraded from the original source file. Here's where A2DP gets nasty. It takes this degraded uncompressed file, and compresses it again, this time using a particularly crude compression scheme, SBC, and what you are left with after wireless transmission and local uncompression in the speaker is an audio file that is riddled with tandem artifacts from daisy chaining multiple lossy encode/decode cycles. Nasty.

WWJD

Now if Apple increased the bitpool, what would happen? Would this solve all the issues with current BT audio quality? Not really. Audio quality would improve, but likely only slightly, because you still don't conquer the tandem artifact issues. Transmission range would decrease and power consumption would increase – owing entirely to the increased use of bandwidth and its increased transmission duty cycle required to ship more data, nominally.

Practical remedy

The right answer is to support MP3 or AAC via Bluetooth – possible and feasible because as mentioned, either are supported optional codecs for A2DP. This means you would not have to decompress a file that is already in the format you are sending over the air. You send it over in its orginal compressed state, then you decompress it once at the receiver. There are some non-dealbreaking implications that must be considered:

1. The receiver must carry the cost of a royalty in order to decode the Mp3 or AAC. That's a bummer for accessory makers. It's not big, but it also hard to get paid for by the consumer, so it eats right into margins. What ends up happening is accessory makers will choose to only support the optional codec in a premium product offering, and run the risk of embedding the low-performance SBC option in entry level products or leaving it out altogether cause it more or less sucks.


2. It is difficult to support BOTH Mp3 and AAC, meaning Apple would likely choose to support AAC as this is the format they sell via iTunes, and so it would make sense that they would want to offer the best audio experience with the format they purvey. This is also something of a bummer for consumers who for the most part still trade and burn in mp3.

Bottom line

• My recommendation as a product developer, but more importantly as a consumer, is that Apple supports MP3 as an optional A2DP codec for the iPhone. I'll take AAC as a second choice... but it's more evil as there is so much music I simply won't convert to AAC, and I will resent having to buy all my music I want to enjoy wirelessly from iTunes.


• Consumers will reject the audio quality currently offered in the iPhone's A2DP standard implementation.


• Accessories will lack efficacy in their wireless audio feature, and the brands that do this will be at risk of taking the heat for the poor performance. This will hamper implementation of the feature in the accessory space.


• These last two bullets, unaddressed, are the two major factors why I predict Bluetooth stereo audio will fade into history, which is sad, because there are dozens of engineers who've worked very hard to get it so close to the original vision's intent. To see it still fall short is depressing.

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Related articles from wirelessaudioblog.com: here on announcement, here on BT headphones.

Everything USB reviews the Creative HS-1200 wireless gaming headset

Overall, a very good review of the Creative HS-1200 wireless gaming headset. Eric's conclusion was balanced, and mostly positive:

Overall, the HS-1200 gaming headset comes out on top: it gets the job done and does it efficiently and effectively over long hours without making you wish for an ear massage. However, Creative's wireless gaming solution - and therefore any product based on X-Fi - still needs work in a few key areas: product-specific documentation and software programming and Creative's house brand of surround emulation all need work. This product gets my recommendation, but a user who spends most of their time gaming and has Windows Vista will probably find this product the most useful. 

[full article]

Logitech ClearChat PC Wireless is Mac OS and Windows "Driverless"

These screen grabs of Logitech's software download support area say it all...

For Mac OS X



... and for Windows,



The ClearChat will be shipping soon, so go check it out if you are looking a wireless headset with Logitech's usual quality.

I've been tinkering... Apple Airtunes is pretty slick

Many folks are familiar with Apple Airport Express and Airtunes. It provides the ability to send iTunes audio from a PC/Mac to speakers that are connected to the Airport Express (which has both a Toslink and a line-level output). I've been playing with the latest variant. With Airport Express w/ wireless N, they've added the ability to support simultaneous receivers receiving the same content. What I call a point-to-multi-point topology.

I've also been playing with Rogue Amoeba's Airfoil which lets me not just play iTunes music, but ANY music from any app on my Mac, or wait for it... a Windows PC. I also have been using Airfoil Speakers which lets me turn any PC, Linux box, or Mac in my house, to an Airtunes receiver. A little tray app runs on that PC, and makes it look like a Airport Express, for example.

I've heard Airfoil lets your send music to Apple TV as well, though I haven't been able to test that. I assume it's as robust as the others have been... and with that little bit of foreshadowing...

It really works well! I love it actually. About my setup:

Audio source:

1. My Macbook Pro running all manner of audio... iTunes, Pandora, Slacker, whatever...

Receivers:

1. My iMac running Airfoil Speakers


2. Airport Express-1 hooked up to Bose SoundDock Portable


3. Airport Express-2 hooked up to Bose Companion 5s.

So a little about Apple Airtunes, which is Apple's proprietary protocol for sending compressed audio over WLAN (AoW). This is all reverse guesstimated based on what little I know about wireless audio...First of all, I call it AoW... I hesitate to call Airtunes "wireless audio", because it only appears that "audio" is being sent wirelessly... what is actually being sent are chopped up AAC (correction via mats) Apple Lossless "data" files with a whole bunch of QoS goop wrapped around it. Strictly speaking, Airtunes relies on a non-linear, asynchronous packet-based transmission scheme, TCP-IP over WLAN. What Apple has created is an extremely broad time-window for synchronizing audio data, creating isochronous behavior using asynchronous foundations and lots of software... that's why you need devices running Apple smarts on either end. Airtunes basically estimates a total time buffer need based on network utilization and bandwidth requirements... creates a time-stamp on the source material... encodes both the stamp and the buffer-time in the data stream... Marker "A"... then it takes the audio data... compresses it on the host side, then essentially transmits the compressed file plus meta information... performs the network transmission, decoding... audio decompression, and again recovering the time stamps and synchronizing them to the device clock and then upon reaching the target time marker extrapolated from the buffer-time... begins rendering the audio at... marker "Z". Or something close to that... I think...

All-in, what Apple does are three important things:

1. Prevents audio dropouts due to periods of reduced network throughput... i.e. it behaves as a buffer. This is important since the WLAN network is a shared network and throughput for audio is not guaranteed.


2. It makes sure all the nodes are playing music in sync to one another, and without time-varying node-to-node drift... This is important in whole-home audio scenarios to reduce echos and unnatural artifacts.


3. To the extent A-to-Z can remain fixed over a playback period... Airtunes also can avoid any audio discontinuities during playback. If the buffer was well-estimated at the beginning of a transmission, then you won't have to resize the buffer and suffer a "skip". One advantage of Airtunes is it can be content aware on the source side, and know when there are silent periods and take those times to reset buffers if need be. Not sure they do this or not.

The result. Fairly rock-solid performance for up to 3 nodes spread across a 80 ft radius space.

Pros

• Apple has been giving much of this functionality for free to those who already buy up Apples stuff. The "converted" are very close to having this stuff working for them.


• Apple software rocks. So this stuff really isn't THAT hard to set up. A little easier than say setting up a WiFi network. A bit harder than hooking up a TiVo. By PC standards... not bad.


• Sound quality and link performance are generally great. For that party mode performance, it works pretty well.

Cons

• Compared to setting up piece of CE equipment, it involves much too much PC time. Installing software, control panels, SSIDs, etc... Advnaced PC user know-how is a must. Even by Mac standards.


• Poor marketing... did you even know this was possible...???? Today???? Like all things, Apple likes to Trojan horse features... then once they get them shaken out by geeks like me, they rationalize them in to shiny new products and services that Stevie J can launch... MobileMe anyone???


• Delay Delay Delay. Buffering and buffer management is the magic to Airtunes... but oh how clumsy it is when you want to adjust volume, or change track... User have to check their audible feedback expectations. Usability nightmare. And what was strange was the more I use this system... the more I notice the delay time.... and of course the more it annoys the shit out of me.


• Cost!!! If you aren't a Apple hardware dork yet. Be prepared to dump $99 for each Airport Express. Add to that the cost of the speaker system you need to connect to it. Rogue Amoeba software is a great convenience, but it ain't free... not bad though to be honest. Airfoil is about $25 per seat. Airfoil Speaker is free... but the computer it runs on is not!

Overall Grades:

B+ for Apple - for giving us a platform

C for Airtunes - for working ok, but using WLAN... a terrible, terrible transport.

A for Rogue Amoeba - for exploiting a platform to the fullest and making nice software that just works.

The Logitech's ClearChat Wireless PC Headset has been a long time coming...

As chopstickhero so eloquently posited,

this is a product that makes you think "why didn't i think of that?"

Well the folks at Avnera did (way back in 2004!), and we made a single chip that will bring devices like this (and more) to market for years to come, at prices consistent with any other common PC accessory.

Logitech, the number one PC accessory maker in the world, also saw the possibilities right away. At Cebit, Logitech launched the ClearChat Wireless PC Headset.  We've been waiting for this meticulously designed headset to hit the streets. Looks like we are a few weeks away from it being in stores. This is really exciting, because Logitech is the first customer of ours to take our core chip-set and then, on their own, set out to design a world-class product around it. It has been a long time coming, but we've now seen why. Logitech pays attention to every detail, and does take their time to widdle away design risks and functional quirks to arrive at a product that is well-though-out and with some clever details that differentiate it from what else is out there, wired or wireless -- Logitech brings crisp, classic industrial design, materials with great feel, and ergonomic expertise to yield probably the most comfortable headset I've worn, including those from Logitech's wired product-line. Among other cool tricks is the microphone boom that illuminates when muted, so people around you can learn when they can talk to you without being heard, and to remind you when it's prudent to curse the folks on the other end of the call.

People will ask, can't Bluetooth do this? The short answer is no.

They will say, "if it isn't Bluetooth, I don't want it." The consequence is they won't be able to use one of the most practical accessories for the PC to come along in years.

You see, BT does not deliver:

• The audio quality of uncompressed PCM 48 KHz audio. This headset delivers 1500 Kbps audio, BT only 320 Kbps.


• The fixed latency of an isochronous audio signal path - with an end-to-end delay that is less than one frame of video. This means you will hear the bullet shells hit the floor when you see them hit the floor.


• Full duplex stereo and voice for gaming. With BT you only get mono voice quality audio in both directions when you give up the stereo. And there is no software out there today that robustly manages the profile switching necessary to put the BT device in the right mode for the application at hand.


• Zero installation steps. ClearChat is Plug & Play with Mac OS, Windows XP and Vista, UPDATE: and very soon Ubuntu

While the majority of computer gamers will probably (rightly) say this thing is great for World of Warcraft or whatever, the applications that I use my wireless headset for (in order of frequency) are:

1. Making calls and attending conference calls via Skype


2. Listening to music on Pandora or Slacker while I work on my PC


3. Watching my Slingbox on Slingplayer

Rock on.