Gallery

Bluetooth madness

Posted on 16 Jan 2008 at 16:19

Paul Ockenden looks at the options available for making and taking calls when driving, and also examines a wireless security solution.

'Ear 'ear

The other type of Bluetooth hands-free device is the portable sort that typically goes in your ear or sits behind it. I've written about these before and my advice remains the same - avoid the cheaper models. I've tried several now and the results are nearly always awful. There are three good models, however, that are worth buying:

Jabra's BT5020 is a great all-round behind-the-ear model, with clear audio, a respectable battery life and even a "vibrate" function. I find it very comfortable to wear on long journeys.

RIM's HS-655 will work with any phone, but when paired with any BlackBerry running OS 4.2 onwards the link between the phone and the headset employs 128-bit encryption, which is obviously great for applications where security is important.

Sennheiser's VMX100 is a device that I haven't used myself, but I've called someone else who was using one and the clarity was simply phenomenal, almost as good as speaking to them on a landline even though the person in question was hammering down the motorway in a fairly noisy car. The only slight snag is that the VMX100 costs about £70, but if you want brilliant audio quality it's a difficult one to beat.

There's a problem with all these personal hands-free devices, though, and that is unless you configure your phone properly they're not actually hands-free at all. If you need to press a button behind your ear to answer or place a call you're actually breaking the law, since the only buttons you're legally allowed to press while driving are those fixed to your car. People using behind-the-ear devices have already been prosecuted, yet mobile phone chains are still persuading buyers that such devices are legal.

One final word on Bluetooth audio, which goes way beyond the requirements of making phone calls in your car, comes from reader Quentin Howard, who writes: "I'm a radio broadcaster by trade, and we have a need for low-latency, transparent compressed digital audio. For years, we've been using something known as apt-X between studios and to feed transmitters. It was developed at Queen's University, Belfast, and is now developed and marketed by APT Ltd, a Belfast-based company. I'll declare an interest here - although my 'day job' is in digital radio, I'm also a non-executive director of APT Ltd.

"So what's the problem? The current standard audio codec used in the A2DP Bluetooth Advanced Audio Distribution Profile is SBC (SubBand Coding), but that isn't sufficiently 'clean' for high-end audio applications such as wireless hi-fi headphones, surround-sound wireless speakers and so on.

"So why not use another established and high-quality codec, such as AAC? Well, three reasons:

"First, fragility. The RF modulation and error-correction facilities in Bluetooth aren't optimised for transmission of complex audio codecs (SBC is relatively simple), which translates to more forward error correction, more RF bandwidth and increased vulnerability (thus audio glitches and dropouts), particularly under marginal reception conditions.

"Second, latency. MPEG-derived audio codecs (in fact, perceptual codecs per se, such as Dolby, Sony ATRACS, Microsoft ASF, AAC) all have relatively long encode/decode processing times, typically 100 to 300ms. Not a problem in itself, except that the time taken for audio to reframe and recover from an RF glitch is unacceptably long. There's also an issue of how gracefully the audio degrades and recovers (does the audio just mute for 300ms or are dropped audio frames repeated, like a sticky CD?). More of a problem, though, is when video lipsync is required. If the audio delay is more than one or two video frames then it becomes unwatchable. This is a problem for both mobile and fixed devices, because the Bluetooth path to all sorts of headphones or wireless speakers introduces an unknown and unpredictable codec delay.