What is TWS? How does it work and what are its advantages?


Since the iPhone 7 appeared, back in 2016, more and more mobile phones do not have the 3.5 mm headphone jack. Because of that, in recent years the Bluetooth headset market has seen spectacular growth. This has allowed the development of new technologies and protocols, based on Bluetooth, which expand its uses and functions. Among them, one of the most prominent is TWS technology, but what is it and how does it work? And what are its advantages and disadvantages?

What is TWS technology?

TWS (True Wireless Stereo) is a technology that allows two audio devices to be paired through Bluetooth connection; and in this way to be able to transmit the left and right channel separately to achieve the stereo sound.

Bluetooth Wireless Vs Bluetooth True Wireless

In the world of Bluetooth headphones there are currently two widely used terminologies: Wireless and True Wireless.

Wireless headphones, also called wireless headphones, are those that do not need a cable to connect to the audio source, but have a cable that connects the left and right headphones. The cable can be seen in the in-ear headphones or it can be hidden in the headband of the on-ear headphones

True Wireless headphones don’t have any cables, not even between the headphones themselves, which makes them more comfortable.

How does TWS technology work?

TWS technology-based its operation on three devices:

The player: this is the original source from which stereo sound is emitted through the Bluetooth connection. It is usually a mobile phone, a computer, etc.

The master device: This is the Bluetooth device, usually a headphone or speaker, that connects to the player from which it receives the full Bluetooth signal (left and right channel). It also connects to the slave device, sending it the audio signal to be played (the left audio channel)

The slave device: connects via Bluetooth to the master from which it receives the left audio channel.
In the TWS headset world, when there is no slave headset, the master works in mono mode.

Master and slave devices are automatically paired via Bluetooth. Once paired, they send a few messages back and forth and calculate the time it takes for a message to go and return.

In louder environments, this time may be longer as Bluetooth devices have to “wait their turn” to broadcast.
Once the time it takes to go and return the signal between the master and slave devices is known, it is divided in half and the time it takes for the connection to go, the delay time, is obtained.

When the Bluetooth audio signal (A2DP) arrives from the phone to the master device, the master device will send the left channel signal immediately to the slave device, but it will wait the calculated delay period before playing it, so that once the signal reaches the slave device, both are synced and play simultaneously.

As we can see, the master device has to manage two Bluetooth connections simultaneously, which affects sound quality and battery consumption.

The Bluetooth protocol has a fairly limited connection speed. For example, the latest version BLE 5.0 has a data transfer speed of up to 2 Mbps, this being in ideal conditions. While the older versions of the protocol have much lower speeds.

Therefore, the master device will have limited bandwidth, since it has to make two simultaneous connections: one to the player and one to the slave device.

So, if the Bluetooth audio quality with a single connection is already quite fair, we can imagine that with two connections the quality will be even worse.

Also, since you have extra work to do to keep both connections active, your power consumption will be higher and your battery will drain a little faster.

Advantages of TWS headphones

Free of cables and ties: TWS earphones are very comfortable. It is not until you try them that you realize how much you hate the cables of the rest of the headphones.

Sufficient audio quality: it should be noted that the old versions of Bluetooth were much more limited in terms of data transfer capacity, but the new versions are much more capable and can offer quite good audio quality (even audio high resolution in some cases). New devices that support one of the latest Bluetooth versions combined with aptX HD or LDAC codecs can offer very good sound quality.

Low prices: Although the price depends on many other things (build quality, durability, size, battery life, etc.) TWS devices use very popular and cheap technologies and components. So it is possible to find TWS speakers and headphones for very reasonable prices.

Easy to set up: TWS devices only need to be able to connect to each other and to do this, it is enough to keep them at a close distance.

Disadvantages of TWS headphones

Inferior sound quality than wired devices: Although Bluetooth is improving every day, there is still a noticeable difference between the audio quality of a TWS device with a wired one (for the same price). In addition, the maximum volume is also lower.

Autonomy: TWS headphones make more intensive use of the Bluetooth connection, so their autonomy is less. In addition, we cannot use them while they are charging because for this they have to be put in the charging case.
Useful life of batteries: rechargeable batteries have a limited useful life and with each charge cycle, we deplete it.

It is true that they will last us a couple of years, but we must bear in mind that once we exhaust the life cycle of the battery, the headphones will not help us since changing the battery is practically impossible.

Latency: Due to the way they work, TWS devices have more latency than normal Bluetooth devices. Fortunately, the difference is usually negligible in most cases.

Still, Qualcomm is developing a new version in which the two devices will connect directly to the playback source. This reduces latency and also reduces power consumption on the master device.

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