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-   -   Psychoacoustic bass enhancement (http://www.diyaudio.com/forums/minidsp/232382-psychoacoustic-bass-enhancement.html)

Saturnus 19th March 2013 08:56 PM

Psychoacoustic bass enhancement
 
Hi

For a new project of mine, I'd like to know if a psychoacoustic bass enhancement plug-in exists for the miniDSP similar to SRS TruBass or AM3D PowerBass plug-ins for Sigma Studio. Or if it is indeed possible to make such with miniDSP.

Given that the original patents for the technique expired between 2006 and 2008, there should be no problems implementing it.

To give a brief overview, the technique uses the psychoacoustic effect of missing fundamental to generate a perceived bass response that goes deeper than the speakers are capable of reproducing.

Technically, it isolates the incoming signal below that which the speakers can reproduce. Generates harmonic frequencies of these. At least 2nd and 3rd harmonic frequencies are needed but including 4th harmonic frequency will greatly enhance the effect. Even 5th harmonic is used in some implementations. The harmonic frequencies are then attenuated to -6dB (2nd), -12dB (3rd), -18dB (4th), and -24dB (5th) of the original filtered signal. The fundamental frequencies are filtered away from this signal with at least 24dB/octave filter before being mixed into the original signal.

It's important to note that the original signal is not filtered at all at this stage. The generated signal is just added to the original signal.

Any ideas?

mattlong8 19th March 2013 10:36 PM

To my knowledge it does not. However the ADAU1701, the processor used by the minidsp, has many options for LF band extension so it's possible that they could implement it if demand is high enough. PM me if you have any questions on Bandwidth Extension I've been studying it in detail recently.

-Matt

Veloxy 16th October 2013 11:29 PM

How did it go?

bentoronto 29th October 2013 05:10 PM

Interesting idea but I am puzzled.

Say you want to hear an organ pedal note but the fundamental note is below the range of your subs. The harmonics are already present in the recording (duh) and you brain is already "hearing" fundamental note that your subs aren't playing.

So why would you need to add anything?

Of course, lotsa fun boosting the bass and this method may just be a wisely configured way to do it compared to just torquing the whole range.

Ben

Bob Brines 29th October 2013 10:45 PM

Psychoacoustic bass enhancement is dependent on the first overtone being present, and with the very small and poorly designed computer speaker that SRS etc were designed for often couldn't go that deep. Then again to the young and impressionable, bass = kick drum = ~80Hz. That's more doable. Put a 6dB hump around 80Hz and suddenly you have "great bass" and lost of "slam". Do that on decent speakers and organ music and it is going to sound truly weird.

Bob

tomchr 2nd November 2013 09:14 AM

I believe the technique is called harmonic extension.

~Tom

bentoronto 2nd November 2013 10:20 AM

In Wikipedia, under "bandwidth extension," I found this:

"Bass enhancement of small loudspeakers

Most often small loudspeakers are physically incapable of reproducing low frequency material. Using a psycho-acoustical phenomenon like the missing fundamental, perception of low frequencies can be greatly increased. By generating harmonics of lower frequencies and removing the lower frequencies themselves the suggestion is created that these frequencies are still remaining in the signal. This process is usually applied through external equipment or embedded in the speaker system using a digital signal processor.

High frequency response can also be enhanced through generation of harmonics. Instead of mapping frequencies inside the reproducible region of the speaker, the speaker itself is used to generate frequencies outside the normal reproducible region. By boosting high frequencies and overdriving the speaker or amplifier slightly, higher harmonics can be generated."

Seems to explain it all. Except for my earlier question. But to answer my own question, if you are playing "computer" music (as compared to simulated real music), you may well have only a fundamental tone present and no naturally occurring partials. In that case, a DSP introducing partials of the unreproducible fundamental can do the trick.

Except for the sternum shaking thrill of real organ music, you can enjoy the full bass-like experience of organ music on speakers with little output below maybe 60 Hz.

Ben

Soldermizer 3rd November 2013 01:17 AM

Interesting. new to me. I am more interested in bass synthesis, since in my experience the bottom octave or two even is absent in nearly any music prior to 1990.

Saturnus 6th November 2013 08:41 AM

Quote:

Originally Posted by bentoronto (Post 3684217)
So why would you need to add anything?

Because you need to add harmonics in a specific pattern when you remove the fundamental. This added harmonics is on top of the existing harmonic content.

The specific pattern require the 3rd and 5rd harmonics to be slightly emphasized over a normal harmonic decay. In practice this is most often realized by limiting the harmonics to 5th as the highest and using a lower harmonic decay of h=0.707 instead of the natural h=1.000 of a sawtooth-like signal (which is what a sinus signal overlaid with harmonic content most resemble).

bentoronto 6th November 2013 09:55 AM

Quote:

Originally Posted by Saturnus (Post 3693115)
Because you need to add harmonics in a specific pattern when you remove the fundamental. This added harmonics is on top of the existing harmonic content.

The specific pattern require the 3rd and 5rd harmonics to be slightly emphasized over a normal harmonic decay. In practice this is most often realized by limiting the harmonics to 5th as the highest and using a lower harmonic decay of h=0.707 instead of the natural h=1.000 of a sawtooth-like signal (which is what a sinus signal overlaid with harmonic content most resemble).

What research underlies your belief that you need that "specific pattern" that is different than what is already present on recording? Wouldn't you think a recording of a sound ought to have the harmonics already present that correctly help your brain imaginatively recreate the fundamental?

Ben


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