Bluetooth Lip Sync Delay and Allion’s Solutions

Allion Labs / Felix Kao

2018 marks the twentieth anniversary of Bluetooth technology. At first, Bluetooth was utilized by Ericsson as a transitory technology in the 2G dial-up era of Modems. Over the course of years, Bluetooth has eventually become an irreplaceable hegemony of Personal Area Network.

Nowadays, many people use Bluetooth to play music wirelessly. Additionally, with Apple terminating the design of the 3.5mm plugs, Bluetooth earphones and speakers have eventually become consumers’ first choice when it comes to music playing.

The latest Bluetooth 5 has twice the transmission speed, four times the transmission distance, and eight times the transmission volume compared to the previous generations while having low-energy consumption. This greatly enhances the delay and endurance of Bluetooth earphones, making them the perfect gadget for watching videos, speaking on the phone, or listening to music.

Bluetooth earphones and speakers have a wide range of  price. The prices of Bluetooth earphones, speakers, and amplifiers can range from two-to-three hundred to several thousands (NT dollars).  Research shows that in addition to the manufacturing costs of driver units and new noise-canceling and pressure-reduction in overhead earphones, the audio codec supported by Bluetooth modules themselves are one of the main reasons for this wide price range.

However, consumers are usually uncertain whether there is a positive correlation between price and the Bluetooth functionality and quality.

Taking Lip Sync delay as an example, we will help you overcome this annoying problem when using Bluetooth products. Unsynchronized image and sound is one of  the biggest issues that could happen during Bluetooth connection and transmission.

Allion provides a relatively objective measuring method to ensure that vendors can produce high-quality products within their budgets.

Allion’s testing equipment:

  1. Audio source (with built-in Bluetooth): Laptop, tablet, cell phone, television
  2. Bluetooth transmitter supporting different coding: SBC, Apt-X, Apt-X Low Latency, Apt-X HD, etc. s, speakers, or amplifiers
  3. Allion® Audio / Video Sensor and
  4. Audio Sink: Bluetooth earphone Lip Sync Fixture
  5. Oscilloscope
  6. Corrected synchronized audiovisual files

Figure 1

First, install the Audio and Video Sensors onto the Bluetooth device and the monitor, respectively. Then, connect the sensors to the Lip Sync fixture developed by Allion. The information collected by the sensors will be converted into digital signals through the Lip Sync fixture, and will be sent to the oscilloscope for analysis.

We play the corrected standard and synchronized audiovisual files to measure sound delays. In Figure 1, the yellow dotted line indicates the start of images, and the green line indicates the sound waves of the video. In this experiment, there is an audio lag as indicated by the oscilloscope. The duration where the green line turns from a solid line to a wave is obviously longer than the yellow line. The time difference can be used to measure the magnitude of the Lip Sync delay.

With different pairing combinations, Lip Sync delays under different conditions can be validated and compared as follows:

In the first combination, most laptops, tablets, cell phones, and smart TVs sold on the market have built-in Bluetooth modules. However, Bluetooth music connectivity is processed by the A2DP (Advanced Audio Distribution Profile) contained in the operating system’s Bluetooth stack. With different A2DP versions and the variety in underlying protocols such as AVDTP and GADVDP supporting functions, transmission efficiency and codec support capability, also have a degree of difference.

Because of this, the Bluetooth Devices Library in Allion’s testing laboratories periodically purchases different brands of Bluetooth devices as test beds to validate the degree of Lip Sync delay.

However, A2DP usually only supports the most basic SBC codec, some of the more advanced codec need to be tested using the second combination. With Bluetooth transmitters that support different codecs, the second combination can not only validate whether the Bluetooth earphones can support their claimed codec but can also further validate the improvement of the Lip Sync delay using an advanced codec. Take Qualcomm’s Apt-X as an example. In an ideal situation, it can largely reduce the occurrence of Lip Sync delay.


There are many factors that could affect Lip Sync delay. For example, internet environment, music player,  coding efficiency of media contents, and external signal interferences and buffering methods can all lead to unsynchronized audio and image.

As a Bluetooth testing lab with experienced engineers and professional measuring equipment, test fixture, and a grand variety of Bluetooth devices libraries, Allion can execute comprehensive evaluations of product performance, thereby helping Bluetooth vendors to precisely decide  their market positioning and pricing, as well as bringing consumers the best user experience.