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This module discusses discusses the primary detection methods used in a real-time laugh track removal system. It is part of a larger series discussing the implementation of this system.


Based on the distinct time-domain characteristics of a laugh track, it is possible to use a simple method to detect such sounds. Our primary detection method uses the envelope of the input signal to find laughs.

Finding the envelope

Method 1

We used two methods of finding and smoothing the envelope of the input signal. In the first method, the magnitude of the input signal is fed into a low pass filter and then squared to obtain the envelope. The filter is a 1000-point fir, linear phase filter generated by MATLAB. The method is simple and easy to implement, but not very efficient.

Method 2

Another method of finding the envelope of a signal is by using the Hilbert Transform. The Hilbert Transform shifts all the positive frequencies in a signal forward by pi/2 and all the negative frequencies backward by the same amount. The envelope may then be calculated by taking the square root of the sum of the squares of the Hilbert transform and the original signal. The Hilbert Transform is calculated by taking the FFT of the input signal, multiplying the positive frequencies by j and the negative frequencies by–j, and taking the inverse FFT. As in the first method, the envelope needs to be smoothed for further processing by low-pass filtering.

Locating laughs

Once the envelope of the signal is found, laughs are detected by a threshold system. The location routine iterates through the samples of the envelope looking for values above a given amplitude threshold. Once this threshold is reached, the routine continues, tracking how long the envelope stays above a second amplitude threshold (lower than the first). If this width reaches a given threshold, the part of the signal from where its envelope rises above the first amplitude threshold to the part where its envelope drops below the second amplitude threshold is flagged as a laugh.

Original signal with laughs highlighted
Envelope of signal with amplitude thresholds
Regions of input signal flagged as laughs
Signal with laughs removed


Our primary detection method gave us good results for the sound clips we used (sitcoms with audio tracks consisting mostly of dialogue and laughs). It does however have a few shortcomings. This method has trouble detecting laughs of low volume, and tends to cut out other sounds that overlap with the laughs. Additionally, it has trouble finding precisely the beginning and end of laughs, due to variations in the envelope shapes of different laughs. We had very little trouble with false positives in the clips we tested, however more sophisticated methods would be required to distinguish between laughter and other sounds with similar time-domain characteristics (such as applause).

Questions & Answers

what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
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Source:  OpenStax, Elec 301 projects fall 2007. OpenStax CNX. Dec 22, 2007 Download for free at http://cnx.org/content/col10503/1.1
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