What is the nature of "tunnel echo"?

I have several audio clips which have been repaired by Sound Cleaner, Adobe Audition and RX 4. Much to my dismay, there is a remaining “tunnel echo” (does it have a nomenclature, official name?) which sounds like the person is speaking though an empty tube of toilette paper (or aluminum oil).

We can place a robotic lab on Mars and we cannot get rid of that sound?

What is its mathematical description or nature?


We can put a man on the moon…

One of the problems of processing a sound clip is overdoing it. You know you went too far when you get that talking into a wine glass effect. If you get that, trash that clip, go back one step and recorrect the work this time with not so much processing.

You can’t “clean” or reverse the damaged clip.


I am mystified by this technology. During my EE studies, after doing my share of Fourier Transforms, I arrived to the conclusion "All one needs to do is apply the correct filter (low pass, high pass and bandpass). Little did I know…

A couple decades later, in which I have not done anything remotely closer (and thanks to the advanced in GUI applications), I have become fascinated with this specialty. Well, let’s go to the beef.

Find attached a sound clip:

(1) Before being processed by Sound Cleaner
(2) After being “repaired” (and yet, injured in a sense). A disturbing “tunnel echo” remains

Additionally, I included time & spectral waveforms.
After-Time Domain.png
Before-Time Domain.png

I was beginning to suspect as much, as soon as I saw the time and frequency curves, before and after.

During my original post, I was judging only with my under-capable ear (let’s just say that musical talents were never a strong in any of my family members). In my naiveté I figured: “Sounds like an alias, a quick filter should take care of that!”.

We can clearly see that a big chunk of information is gone. Notice the big “bite” missing in the spectral curve!
After-Frequency Domain.png
Before-Frequency Domain.png
After-Time Domain.png
Before-Time Domain.png

For completeness, find attached the spectral curves.

After-Frequency Domain.png
Before-Frequency Domain.png