Room Shaper

 

Room Shaper is new innovative correction solution focusing on room resonances. As the involved technology is not standard filtering, we can only offer it as a separate plugin. You can read the page below to get a better understanding of the concept and advantages.

 

The plugin and user manual can be downloaded from here

You can test it (demo mode) and use the contact form for registration.


Room modes and how we can limit their negative impact on listening experience with innovative digital processing

Typical living room and home theater acoustics are dominated by modal resonances in the low frequency region. Room modes are created when a sound wave travels between two opposite boundaries and become a standing wave. The room geometry and its absorbent characteristics are defining the distribution and characteristics of the modes. There is a huge amount of information available on small room acoustics on the web and the purpose here is not to replicate it, but explain how our new digital correction addresses this issue. Why are modal resonances an issue for hi-fidelity reproduction?

Modal resonances have a negative impact on listening experience for two main reasons.

 

At first, they modify the magnitude response of the musical message by creating large peaks or dips at different frequencies. This is easily visible on a room frequency response like this one:

The boosting at some frequencies comes from a temporary storage of acoustic energy that will require a certain time to dissipate once the sound energy source is stopped. We call this the mode decay time. Short decay times are usually not problematic, as the primary signal will mask them. On the other hand the remaining energy from a long decay resonance will be heard and degrade the timing of the original musical message.

 

A waterfall or spectrogram presentation of a room transfer function gives a direct visualization of both issues, tonal modifications and uneven decay timing :

In order to ease the comparison between different rooms or correction, we will use the overall energy decay curve as it present valuable information with a single curve. This curve show how fast the acoustic energy is decreasing after the sound emission is stopped:


The problem of room modes and their effects on the correct reproduction have been subject of many research and proposed solutions range from room aspect ratios guidelines, acoustic treatment, loudspeaker placement, multiple loudspeakers arrangement and active correction with digital signal processing. When severe acoustic treatment is not possible, digital processing offers the best alternative (acoustic treatment for low frequency range is a challenge)

If we put aside the active control of multiple subwoofers, the standard signal processing techniques to address room modes are based on filtering. The most common approach is to flatten the magnitude response. While this correction address the tonal impact of resonances, is it as well addressing the timing aspect?

The answer is yes and no !

From a pure digital signal processing theory, the magnitude equalization will improve the timing response when the room transfer function is of minimum phase type. Minimum phase means that the timing of the response is fully linked to the amplitude response and if the amplitude is even, the decay time will be the shortest possible one. So correcting the amplitude will improve the timing as well.

 

Most of the rooms do not have a pure minimum phase response and therefore the magnitude equalization will not improve the timing to the full potential. In some cases, the resonances are less “sharp” and magnitude correction will not improve at all the time response. Those cases are illustrated by following graphs (the blue curves correspond to the timing response of the room after correction if the room response was purely of minimum phase type)



From we have seen there is room for improvement starting from a magnitude equalized room. This is what we do with our innovative solution.

The key idea is to characterize the room response and identify the frequency areas where the decay times have a negative impact. We process the input signal to isolate sound events, for instance a long bass note or a single kick drum.

 

If the sound event is overlapping with modes with long decay, we modify it to reach the same psycho-acoustic quality as if played in an even damped room. Combining such approach with magnitude equalization greatly improve listening experience as if the room disappeared !