What is aptx and latency?

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

  1. Aptx enhances the sound quality to Hi-Fi quality. Note that aptx must be incorporated in both sender and receiver to obtain the enhanced sound quality.
  2. Aptx reduces the “conversion time” – also referred to as “delay” or “latency time”. When you have only one transmission channel from sender to receiver, “latency time” is of no importance and can be ignored.

NOTE: There are two types of aptx on the market. The most common is the one with 100 ms “latency time”. The other type has a “latency time” of only 35 ms. This is the one Telme2 is using in both the Tosblue X and BHX products.

When we have two parallel transmission channels operating 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 X unit 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”.



If two persons are watching the TV, as illustrated above, where one person is using a headset and the other is listening to the TV speakers, then situations like this may be the cases:

  1. If the person is using a headset with the shortest aptx “latency time” – the the two sound outputs will be in sync. Everything is fine.
  2. If the person is using a headset with a longer “latency time” – there will a a delay. How noticeable this delay will be depends mainly on the following:

– If the headset has good passive noise reduction – so the sound from the speakers is hardly is heard inside the headset – then it is OK.  If not, some measures must be taken.

What is Latency:

“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 X unit 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 as illustrated here:

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

What is aptx:

Aptx is an anvanced audo compression algoritm. The technology is used in the signal conversion process. Telme2 uses the shortest latency aptx technology. (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 small delay will not be noticed.

When you use the Tosblue X unit connected to your TV, then synchronization of sound and picture are important.

Let me explain:

The TosBlue X unit is transmitting sound from your TV to a bluetooth headset. If the TosBlue X unit and/or headset does not use aptx technology – the sound will be delayed in the conversion process in both units. The sound from the internal TV speakers and the sound in the headset may not be in sync at the receiving end. If the delay is considerable, you may also notice that the sound in the headset is not quite in sync with the sound from the internal speakers of the TV.

Now, on most new TV’s you may adjust the output timing on the Toslink output. Then you may adjust until the timing is in sync,  you will be in good shape. This wayany bluetooth headset may be used.

Another way is to use Telme2’s BHX Hi-Fi  steroeo headset with next to no latency time. Then no adjustment is required. You will receive fantastic sound with no delay.

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