Eilex PRISM Stratos™

Two-Channel Immersive Sound Process

  • SHM (Spherical Head Model)(1) based HRTF(2)
  • XTC (Crosstalk Cancellation)(3) Process
  • Natural 3D Sound with Height 3D
  • Wide and Realistic Sound Image
  • Consistent Dialogue
  • APVD (Acoustic Power Volume Density) measurement and equalization by Eilex PRISM
  • Suitable for TV and Sound-Bar

Today’s immersive audio systems require surround speakers as well as wall- and ceiling-mounted speakers to achieve their effects. Such systems are often impossible for customers to set up in their homes. To address this limitation, some manufacturers have put up-firing speakers in their TVs and sound bars — the idea is to utilize the reflected sound to simulate ceiling speakers. However, this solution increases the cost of the TV parts, and reflected ceiling sound will be far from optimal.

Additionally, these systems also require movies and other content to have many audio channels to properly create their effects.

Eilex PRISM Stratos™ creates immersive sound from regular 2-channel audio on TVs with ordinary speaker systems. Stratos widens the sound stage beyond the physical placement of the left and right speakers, and extends it above the TV picture height.

Eilex PRISM Stratos™ is a combination of Eilex PRISM® APVD (Acoustic Power Volume Density) equalizer and Stratos 3D processes. Stratos 3D does the job of enhancing the stereo image of the input signal. Eilex PRISM optimizes the system’s sound to reproduce exactly what was recorded. (For more information about Eilex PRISM® please see the white paper.)

The Stratos 3D process uses a Spherical Head Model-based HRTF for Cross-Talk Cancellation (XTC). SHM-based HFTF is more versatile than conventional model head-based HRTF.

Eilex PRISM Stratos™ uses regular 2-channel audio materials to achieve its effect.

Left — An audio system without any effects. The listener perceives the sound as coming generally from the center.
Right — The same audio system with Eilex PRISM Stratos™ applied. Stratos creates the perception of audio sources beyond the physical locations of the speakers.


  1. SHM (Spherical Head Model) assumes the shape of a human head to be a sphere when analyzing the three-dimensional sound propagation around it. Since no model will match the shape of every individual’s head, the spherical model makes a good generalization.
  2. HRTF (Head-Related Transfer Function), in the case of 3D sound, expresses the frequency response when the sound from the left or right reaches the other side of the head traveling around the head. It is also affected by torso and shoulders. The measured HRTF belongs to the particular dummy head and does not necessarily match each listener’s HRTF. If it is used in 3D process, the results can have larger offsets.
  3. XTC (Cross-Talk Cancellation) uses timing to stop the sound from the left or right channel speaker from arriving at the listener’s opposite-side ear. This improves the 3D effect.