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Wi-Fi for wireless audio

Why we do not use Wi-Fi for wireless audio

Over the past few years, wireless sound has been developing by leaps and bounds: smartphones without a 3.5 mm output are actively being released, “almost Hi-Res” codecs like AptX HD and LDAC appear, and a lot of cool wireless headphones come out. And they all have one thing in common – they work via Bluetooth. This begs the quite reasonable question: why did you choose this technology, and not, for example, the same Wi-Fi, which again is in most gadgets?

Few Wi-Fi channels

In the 2.4 GHz range, there are only 13-14 channels through which data can be transmitted. In the 5 GHz range, there are slightly more of them, about 50 (non-overlapping 24). It would seem that this eye is enough for all wireless devices within a radius of 10-15 meters in the house (then the Wi-Fi signal usually “does not break through”). But there are two important problems: firstly, the channel width in the 2.4 GHz range is 22 MHz, so the channels intersect: that is, for example, your use of 6 channels means that you will “interfere” with networks operating from 4 to 8 channels . Therefore, usually 4-5 Wi-Fi networks around are enough for your Internet access speed to seriously decrease.

Now imagine that in addition to five routers that distribute Wi-Fi, there will be a dozen more gadgets of users who, in essence, will also distribute it to various speakers and headphones. The result will be a catastrophic drop in speed. And here the question arises: after all, Bluetooth works in the same 2.4 GHz band, why are there no such problems?

The reason here is that BT uses as many as 79 non-overlapping channels with a width of 1 MHz over the entire range – you must admit that it’s much harder to “clog” this connection and its effect due to the low channel width on the Wi-Fi network is minimal.

Noise immunity

Obviously, if we want to get the minimum delay and the highest speed, it is best to choose an empty Wi-Fi channel as far as possible from the busy ones. The same is true for wireless sound: it is obvious that when creating a pair of device-headphones, the most free range will be selected. But now imagine that you are walking along the street with these headphones – there are a lot of houses nearby, and they may well have networks working on the same channel. How does this affect the sound quality, I think, and so it is clear. The way out of this situation is also obvious – a dynamic change of channel to a freer one. But, alas, Wi-Fi is not able to do this: changing the channel from the side of the device will lead to disconnection.

FHSS Devices

But Bluetooth just survives thanks to the fast change of channels: this technology is called AFH (Adaptive Frequency Hopping), and with its help the channel is cleverly changed 1600 times per second to one of 78 others. Why smart? Yes, because AFH quickly detects the channels occupied by Wi-Fi, and does not use them. Yes, this removes some of the range from consideration, but still it’s better than sitting on the same channel forever and listening to wheezing. Moreover, it should be borne in mind that Wi-Fi is slowly but surely moving to 5 GHz, thereby freeing up 2.4 GHz for Bluetooth.

Sound delay

What Wi-Fi, what Bluetooth use packet data, but in slightly different ways. In the case of Wi-Fi, we get several wide “pipelines” that can accommodate several packages together, but you can use only one pipeline. Therefore, if many people use it at once, you will sit and wait until it shows up free space and you can “put” your package on it. The result is sad: in a place loaded with networks, the delay can easily go into the range of 100+ ms, which will be critical for sound.

aptx Low Latency

Bluetooth works differently: you have 79 narrow pipelines that can only accommodate one packet at a time, but you can use either of them. As a result, this allows you to work with a minimum of delays even with the loaded 2.4 GHz range, which is critically important for watching videos or games with wireless headphones.

One device – two Wi-Fi networks

It is obvious that at home your smartphone will simultaneously connect to the Internet via Wi-Fi and stream music to headphones through it. In fact, there are no problems here: there is Wi-Fi Direct, which allows devices to transfer data to each other without any routers and hot spots, which is ideal for transmitting sound in our case. But it is worth remembering that there is only one Wi-Fi adapter in the device, just like the antenna, so you will have to process packets from both networks sequentially. The result will be sad: this is again an increase in delay and a decrease in the speed of access to the Internet.

power usage

Of course, wireless sound is initially aimed at mobile devices, so energy saving is not the last thing that plays here. And here Wi-Fi is getting worse than Bluetooth LE: for example, an unused “blue-tooth” connection consumes about 2.5 mW, when Wi-Fi – up to 30. With active data transfer, BT can consume up to 100 mW when Wi-Fi – up to 500! So in terms of energy saving, Bluetooth looks much more profitable.

Wi-Fi has higher speed – which means you can transmit better sound

In theory, this seems to be true: even Bluetooth 5.0 speeds do not exceed 1 Mbit / s for audio transmission, when for Wi-Fi 802.11ac and 500 Mbit / s is far from the limit. To transmit CD-audio with 16 bit / 44.1 kHz, a bit rate of 1411 kbit / s is required: taking into account that sound without loss of quality can be compressed in half, then to transfer such audio we need a codec with a bitrate higher than 700 kbit / s – for example, the same LDAC has 990 kbps, and is free on Android 8 and higher, so there is no problem with CD audio.

Well, if we take Hi-Res, that is 24 bit / 96 kHz? To transfer it, you need a speed of 4.5 Mb / s already, that is, if you think about double compression, the codec should be able to transfer more than 2 Mb / s – and this, surprise, is twice as high as Bluetooth allows. So for listening to high-definition music, it is definitely not enough (or rather, it will be enough, but 4: 1 compression with data loss will be used, which makes lossless listening meaningless). But with Wi-Fi, there are obviously no such problems – 2 Mb / s has not been considered something transcendent here for a long time. But it should be understood that the vast majority of users use various streaming services, where the bitrate of the tracks does not exceed 320 kbps, and even normal AptX is enough for their trouble-free listening, so this problem only affects a small number of audiophiles.

Why not make a special technology for transmitting wireless sound?

Wi-Fi, as already understood, is poorly suited for sound transmission. Bluetooth cannot transmit Hi-Res without compression. So why not invent a new technology specifically tailored for wireless audio transmission?

The idea, of course, is sound – but practically unrealizable in practice. Firstly, for this technology to work, you need your own frequency range (we don’t want to hear clicks and sound loss, right?), And given that the frequencies available for commercial use vary from country to country, this range should not be one. Given the fact that even with the allocation of frequencies for a fairly important 5G there are enough problems, you can forget about a separate range for wireless sound.

Secondly, even if somehow their own frequency range is issued for this technology, another problem will arise – it will be necessary to produce equipment to work on it. Of course, the easiest way is to place an order with a large vendor, such as Qualcomm. But this is bad luck – he is actively promoting AptX, and is unlikely to agree to make equipment for his “enemies”.

But alright, let’s say such a fantastic option that there are no problems with equipment and frequencies. And here a third and no less difficult problem appears: it will be necessary to write drivers for new adapters for most modern OSes, and convince device manufacturers – not only smartphones and laptops, but also headphones and speakers – to install these adapters in them. Moreover, most companies should do this, otherwise the technology runs the risk of becoming niche and unnecessary to anyone. Obviously, convincing everyone to switch to a new technology, when for most people and Bluetooth works fine, is unrealistic.

Bottom line – why touch something that works so well

special technology for transmitting wireless sound

What is the result? As a result, we are faced with the good old principle of “work – do not touch”: Bluetooth in its current form is enough for wireless listening to music up to CD-quality, and only a few people listen to music in even better quality. Therefore, “Sinezub” will most likely remain the leading standard for wireless audio transmission in the coming years – it makes no sense to change it, because it will bring many problems, and only a small number of audiophiles with extremely expensive equipment will hear the difference in quality. But, of course, if an increasing number of people begin to listen to music in Hi-Res, then, obviously, there will be progress: although, most likely, everything will be limited to the new version of Bluetooth with an increased data transfer speed, since it is easier to do this than to develop a new technology from scratch.

Sam Richards

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