What is aptx and latency... and why does it matter?

aptX technology is a key words related to the Bluetooth. It is a technology enhancing the standard Bluetooth technology in two ways:

  1. apX enhances the sound quality. Note that aptXmust be incorporated in both sender and receiver to obtain the enhanced sound quality effect
  2. aptX reduces the "data conversion time, also referred to as "sound delay" or "latency  time”. When you have only one transmission channel from sender to receiver, “latency time” is of no consern and can be ignored. However, when more than one parallell sound channal, this is an important issue.

There are two types of aptX versions on the market. The most common is the one with 100 ms “latency time”. The best type has a “latency time” of only 35 ms. This is the one Telme2 is using in both our Tosblue units and BHX headset.

When we have two parallel transmission channels operates at the same time, it is important that they are synchronized, i. e. that the sound output from both channels arrives at the receiving end the same time. Most of us can accept a difference of up to 50 ms (milliseconds) delay between the two channels without noticing any problem. So when the sound arrives within a “window” of 50 ms, we may say that the two channels are in sync. If it is more – like 100 ms - we start noticing the delay.

Telme2 is using the aptx technology with the shortest delay – 35 ms – in both our Tosblue units and our new BHX Hi-Fi Bluetooth headset. When used together, the total delay is about 40 ms, which is within the acceptable “delay window”.



On the illustration above, two persons are watching TV. The older person is using a headset and the younger is listening to the internal TV speakers.:

  1. If the older person is using a headset uses a BHX headset, then there will be practically no  “latency time” – i.e. the the two sound outputs will be in sync. Everything is fine.
  2. Now, you may wonder why the older person is using a headset. If she is hard of hearing she may adjust the sound louder in her headset. The younger person may listen to the TV sound from the internal speakers at a low pleasent level for her. If a headset without aptX is used, a noticeable delay will occur. Hoe annoing this is, may depend on the following:

– If the headset has good passive noise reduction, then the sound from the speakers may hardly be heard inside the headset – then it is almost OK.  The lesser problem is that the sound and Picture is not quite in sync.

More about aptX here: http://www.aptX.com

So what is "latency time":

“Latency time” is the time it takes from signal input to signal output of an electronic device. It is also referred to as “throughput time” of a device. As an example, our Tosblue units receives optical digital signals – also referred to as SPDIF or Toslink signals, from the TV. The unit converts these signals into electrical signals and further into wireless Bluetooth transmission signals.

This process takes some time – referred to as “conversion time” or “latency”. 

Then, what is aptx:

aptX is an anvanced audo compression algoritm. The technology is used in the signal conversion process and is done in hardware, as opposed to software. Telme2 uses the shortest latency aptX technology from CSR. (35 ms)

So why is aptx with low latency so important?

In most cases latency is NOT important. If you are transmitting sound from your smartphone, tablet or PC to our BHX headset – low latency is not important at all. The reason being that the sound path will not be synchronized with another sound path or visual path. So any delay will not be noticed.

When you use the TosBlue units connected to your TV, then synchronization of sound and picture are important.

Let me explain:

The TosBlue unit is transmitting sound from your TV to a bluetooth headset. If the TosBlue unit and/or headset did not use aptX technology – the sound would be delayed in the software conversion process in both units. The result would have been sound delay. If the delay is considerable, you may also notice that the sound in the headset is not in sync with the moving Picture in Your TV.

NOTE also: On many new TV’s you may adjust the output timing on the Toslink output port. Then you may adjust until the timing.. In best case you may be able to compensate for most of the delay and a headsdet without aptX may be used without any timing problems.

However, we recommend to use Telme2’s BHX Hi-Fi  stereo headset with best aptX included. Then no adjustment is required. With the headset upgarded to BlueTooth 4.2, you will be able to enjoy fantastic sound with no delay.

We Call the combination of a TosBlue unit and the BHX headset for tvSoundCast. The tvSoundCast is offered in 3 versiens. Find out which Version is most suitable for you.

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