Speech

Human speech has become a system of communication requiring coordination of voice, articulation and language skills. Voice is produced by the movement of air which vibrates through the vocal cords.

Vocal chords are made of elastic connective tissue covered by folds of membrane. The pitch of your voice is controlled by the modification of the muscles that shorten the cords pulling them tight for high pitch and slack for low pitch.

Articulation is the modification of airflow. Speech is articulated by the movements of the tongue, lips, lower jaw and soft palate. Vowels come from voiced excitation of the voice tract. Articulators are kept static and all sound radiates from the mouth. Nasals are generated when the tongue is raised and the soft palate is lowered which reduces the oral passage. Plosives are generated when the vocal tract is closed by the thr tongue or lips and then the pressure built up is suddenly released. Fricatives are formed by partially restricting the vocal tract by the tongue or lips.

The Moving Image and Video

The first moving image was introduced to the television in 1926 by John Logie Baird. This was based on the old idea of Persistence of Vision (PoV). PoV is the theory that the eye has a retention of an image of about 1/25th of a second and therefore if a secondary image was viewed before this persistence ends then the observer would not notice the change of images.

The image shows an early toy called the Zeotrope which created the illusion of motion. This was invented in 180AD and then a modern version was reinvented in 1833. The viewer looked through the slits and because of the speed at which the images were rotating it created the illusion of motion despite it actually being a series of still images.


This theory is now regarded as the myth of persistence of vision. The more plausible theory now is that there are two distinct perceptual illusions in phi phenomenon and beta movement.

Bitrate is the word used to describe how many bits are required to show a video per second. This can vary from as low as 300kbps sor a low quality video, upto 8000kbps for a high quality video.
Interlacing is a way of getting the best results from a low bandwidth. It is done by alternating showing the odd numbered lines on the television first, then the even numbered lines of the next image at a speed of 25 frames per second. This gives the illusion that the images are moving.
Resolution is the number of pixels a televison can display. When analogue TV was used, typical resolution was 352x288 in Europe. Comparitively, modern televisions can display as many as 1920x1200. DVD quality is typically 720x576 for European televisions, while Blu-Ray and HD provide the highest resolution.

File Format

MPEG-1 - First designed in 1988 was the first decoder and could compress a video to about 26:1 and audio 6:1. Designed to compress vhs quality raw data with minimum loss in quality.

MPEG-2 - The improvement to MPEG-1 and is the format of choice for digital television broadcasters. It actually developed as early as 1990 before MPEG-1 was released.

MPEG-4 - Integrates many features of previous versions while adding support for 3-D rendering, Digital Rights management and other interactivity.

Quick Time - Appeared in 1991 created by Apple almost a year before Microsofts equivalent software.
It can handle playback from VLC and MPlayer both which are PCLinuxOS based.

AVI - Appeared in 1992 by Microsoft. A problem with this format was that it could appear stretched or squeezed during playback however the players such as VLC and MPlayer solved most of these problems. But a massive advantage of it is that it can be played back on almost every player and machine making it second only to MPEG-1.

WMV - Made by microsoft using several codecs and is used for BluRay discs.

3GP - Used for CDMA phones in the US. Some phones us MP4.

FLV - Used to deliver video over the internet and is used by YouTube, Google Video, Yahoo Video, Metacafe and other news outlets.

Intro to Cool Edit Pro

CoolEditPro is a piece of software which allows you to view a sound file in its digital format and then allows you to edit this wave. You can choose from which point you want to listen to the sound file or even select a specific section to play by highlighting the section.

The wave can be manipulated in various different ways such as copying, pasting and trimming the whole wave or selected parts of it. Additionally you can add other waves onto or into the file to extend it. When the wave is open it is possible to change the data about the wave being displayed on the screen such as the time, time signature or changing the scales to allow more accuracy.

It is also possible for the user to zoom in and out of the wave to allow greater detail and closer selections. Other affects available to the user are things such as reverse and invert which change the pattern of the wave and therefore how the wave sounds. The amplitude can be changed which changes the volume of the sound file and can also be faded to allow quieter sections or merges of two sounds. Other features are things such as delay, reverb, echo etc.

Looking at Light

The concepts of looking, seeing and observing are very different. The definitions of looking is readying yourself to see something, seeing is when the eye actually receives light energy and converts it into impulses and observing is when we analyse, interpret and decide what the nerve impulses are i.e. object or an effect.

On cloudy days light appears white however it has a bluish tint. The clouds actually act in such a way that they soften the light and diffuse it, spreading it out.

Front lighting occurs when the light source is behind the person observing the object which evenly lights the object. Side lighting creates strong shadows which emphasizes texture and adds depth to an image. The most dramatic lighting though is back lighting meaning the light source is behind the object creating silhouettes and other interesting effects.

Light

Light is defined as a form of energy detected by the human eye and has been observed to be able to travel as both streams of particles and in waves. Light is different from sound, sound needs a medium to pass through in outer space in order to travel, where as light can travel directly from the sun through the vacuum of space  in order to reach earth.

Light travels as a transverse wave much like a ripple on the surface of the water. It travels at right angles both up/down and right/left from the point of origin. Light works the same as radio waves, each colour is a different frequency and the eye acts like a radio receiver. The frequency range is 400THz (RED) to 750THz (VIOLET).

Light Travels at 300000000 m/s in a vacuum, it slows down a little in air and slows to 2/3rds in glass. The slowing off light in glass makes that material useful for lenses. The frequency is the vibrations per second and the frequency of the lightwave is independent of the medium which its travelling in. The same lightwave would have a different wavelength because the speed of light is slower in glass.

White light is made up of every colour of the spectrum though some colours are more prominent than others.

Above is shown the light spectrum of visible light and then both extremes of wavelength which the eye cannot detect. Each light source has a different reaction to each frequency of different colours. Waves which have wavelengths of longer than 700 nm are infrared and those with wavelengths shorter than 400nm are ultraviolet. 50% of sun energy is visible to us on the earths surface and about 3% is ultraviolet leaving the rest being infrared.

Monochromatic light (single colour) is uncommon however is used in street lighting. Under this type of lighting the world appears to be in shades of grey and completely colourless.

Brightness is measured in candela and lumen by scientists but photographers use light exposure meters that have been set up by scientists. A candela is the power emitted from the source in a particular direction. The  units of candela emitted from a standard candle is 1 candela. A lumen is the total amount emitted from a source irrespective of the the ability of the eye to see it.

Light waves once emitted from the source are transmitted, reflected, absorbed, scattered and refracted. Transmitted light is the same as emitted light, it simply describes the act of the source producing light waves. Reflected light is when light bounces off of a solid object i.e. a mirror. The angle of reflection is the same as the angle the light hits the surface (angle of incidence).

The reflection shown in the diagram is know as SPECULAR reflection however there is also DIFFUSE reflection which happen when the light waves contact a rough surface. The light can reflect in many directions which is known as Scattered light. Absorbed light is light waves that come into contact with a solid surface but do not reflect. Instead they are absorbed and disappear. Refraction takes place when light waves pass into a transparent object and then when they pass back out the other side. It is basically the act of the light bending. When the light waves pass into and out of the medium they speed up or slow down depending on
the speed of light in that particular medium. This explains why it is difficult to see things that are submerged in water and why they appear bent, because the light is bending as it passes from travelling through water to travelling through air to reach the observers eye.

The Inverse Square Law states that the intensity of the light at a point is directly proportionate to the square of the distance from the light source.

Week 7 Lab 4

The aim of this Lab was to take a sound file that I downloaded from moodle and improve the quality of said sound clip. After downloading the wave and opening it in Cool Edit Pro, I began to investigate ways to improve it.

This image shows the final improved sound Wav after a series of small changes. Firstly, I applied a notch filter which I set at 440Hz and 2dB. I also added DTMF Lower tones at 100dB and DTMF Upper tones at 2dB.  I then targeted and zoomed in on the spoken sections, the peaks, and I amplified those sections by 10.98dB. I did attempt to amplify them by more, however, it causes 'White Noise' i.e. a loud continuous noise. Finally, I used the hiss reduction function to clean up the over all quality of the sound.


The second part of the Lab was to edit the .wav to make the speaker sound angry. This was more difficult than the first part of the task and took longer.

I achieved this part of the task by making the start of each word louder but also by gradually increasing the volume of the sentence. The resulting wave of the below steps is shown on the right. Firstly, I individually selected the first letter of each word and increased its amplitude by on 1dB, which was enough to make those letters noticeably louder and more hard hitting. Then by selecting the entire wave I added a gradual amplitude change of 2dB from the start of the sound through to the very end of the spoken section of the file.

Section 3 of the Lab was actually very easy despite it sounding quite difficult. The task was to take the already edited .wav and make it sound as if it was being recorded in a church hall. I edited the improved sound file. Under the reverberation option I could select Church reverb, so I applied this to the entire wave. I then added a bit of amplification to boost the volume slightly after the reverb made the sound a quieter.



The final part of this lab was to add church bells in the distance. I started with the completely edited .wav (shown in green) and I then found an extra .wav of a church bell (shown in red). I duplicated the sound file to double its length so that it spanned the length of the initial sound file. I amplified the church bell .wav by -10dB so that it was quiet in comparison to the other .wav as it was meant to be outside the church that the man is standing in.

Hearing Lecture

 The Ear

Outer Ear - The Pinna and the Ear Canal basically act as a guide to sound waves, directing them down the ear to the ear drum. The Pinna also acts in such a way that it can collect information on the direction and source of a sound wave as it hits your ear. This part of the ear also acts as an amplifier for the sound that you hear. 

The Middle Ear - The sound heard travels down your ear canal to the ear drum causing it to vibrate. The vibration by the ear drum is transferred through small bones called Ossicles, and this vibration causes the Cochlea to vibrate. The vibrations actually reduce power loss in the sound wave and once at the Cochlea is transferred to the fluid medium in the Cochlea. Loud noises/sounds create excessive amounts of vibration in the Ossicles which can damage hearing, therefore, there is a neuro-muscular feedback system in your ear that helps to protects your hearing from damage.

The Inner Ear - Vibrations in the oval window creates waves in the cochlear fluid which in turn causes the cochlear perform a spectral analysis. Sensor cells cause neurons in the auditory nerve to react. The timing, amplitude, and frequency information is taken to the auditory brain stem where neural processing takes place.

Malleus - a small hammer shaped bone also known as an ossicle which is part of the middle ear.

Stapes - Transmits the sound vibrations from the incus to the cochlea.

Incus - Connects the Malleus to the Stapes.

Scala Vestibuli - filled cavity inside the cochlea that conducts the vibrations to the scala media.

Scals Media - Also know as Cochlea Dust, it is also a filled cavity inside the cochlea.

Scala tympani - function is the same as scala vestibuli and is to transduce the movement of the air that casue the vibrations in the ossicles.

Organ of Corti - This section contains the auditory sensory cells. which in turn connect to the brain. This is only found in mammals.

Impendance Matching is a very important mechanism in the middle ear. It transfers vibrations ceated by the sounds your hear from the large tympanic membrane to the smaller oval window in the middle ear. The reason this is vital is that the oval window is low impedance and this is needed as high impedance vibrations of the cochlear fluid will reduce the energy transmitted dramatically to 0.1%.

Auditory Brainstem

The main features of auditory brainstem processing are that there is a two channel set of time domain signals in contiguous, non linearly spaced frequency bands; There is separation of the left from the right ear signals; low from high frequency information; timing from intensity information; re-integration and re-distribution at various specialised processing centres; binaural lateralisation; binaural unmasking; listening in the gaps and channel modelling.

Week 6 Lab 3

Lab 3

The lab this week was to create a wave and then mix different waves together to create a new wave. The waves were created using a fundamental and the harmonics of the fundamental.

Harmonic Number	1	2	3	4	5	6	7	8	9
Amplitude relative to Fundamental	1	0	1/3	0	1/5	0	1/7	0	1/9
Amplitude dB	0		-9.54		-13.9		-16.9		-19.1
Frequency	400		1200		2000		2800		3600

The initial wave (fundamental) was created by setting the sample rate to 8000Hz, 8 bit, mono, the frequency to 400Hz and the duration to 0.02 seconds. This created the following wave :

The fact that I set the frequency to 400Hz, meaning 400 waves per second, and the duration to 0.02 seconds results in 8 cycles of the wave being drawn as 400Hz/0.02s = 8.

Next I worked my way through the chart only creating the odd harmonics as waves i.e. 1 (fundamental), 3, 5, 7 and 9. I created all of these waves individually always leaving the sample rate the same but changing the frequency and the amplitude for every harmonic. I worked out the frequency by multiplication. The 3rd harmonic of the fundamental has a frequency 3 times greater, similarly, the 5th harmonic has a frequency 5 times greater and so on. 

To work out the respective amplitudes of the harmonics I used a simple equation. For the 3rd harmonic I did 1/3, I then took the log of the answer, I then multiplied it by 20 to give me the amplitude.

For the 3rd harmonic of the fundamental the data I input was amplitude -9.54 and frequency 1200Hz, the wave created was:

Similar to the fundamental wave the number of cycles was calculated by dividing the frequency, 1200Hz, by the time which was 0.02 seconds, resulting in 24 cycles of the wave. As previously explained the 3rd harmonic of the fundamental has a frequency 3 times greater therefore the number of cycles of the wave within the same time period is also 3 times higher, 8 compared to 24.

I performed the same operation on the other fundamentals and then I cut and mix pasted them all into one wave. As I did so I noticed that a square wave shape started to take form as I pasted each wave in one at a time. The resulting wave after I pasted all waves on top of the fundamental was:

Part two of this lab was very similar to part one, however, this time after creating the fundamental tone I was to create the 2nd harmonic upto the 5th harmonic and merge them with the fundamental pure tone. The table of data was worked out the same as it was above and was as follows:

Harmonic Number	1	2	3	4	5
Amplitude relative to Fundamental	1	1/2	1/3	1/4	1/5
Amplitude dB	0	-6.02	-9.54	-12.04	-13.9
Frequency	400	800	1200	1600	2000

The initial fundamental pure tone was created using the same parameters as I used above;8000Hz, 8 bit, mono, the frequency to 400Hz and the duration to 0.02 seconds. The wave created therefore was identical to the fundamental wave at the top of the page. However, because I am now adding in all the harmonic waves instead of just the odd numbers the resulting mixed wave is significantly different from that shown above.

The wave created is almost like mountains in a way. Also, as there are completely vertical inclines on the wave it makes it more like a digital wave as opposed to an analog wave. A digital wave only has 2 options, 1 or 0/ on or off, although it is not quite as simple a wave as that it is getting close to it.

Tutorial Week 2

Q1 In a recording room an acoustic wave was measured to have a frequency of 1KHz. What would its wavelength in cm be?

The wavelength is 0.333cm. I worked this out by doing the following calculation :

v = fλ

λ = v  = 333   = 0.333cm

       f     1000

Q2 If a violinist is tuning to concert pitch in the usual manner to a tuning fork what is the likely wavelength of the sound from the violinist if she is playing an A note along with sound from the pitch fork?

Q3 If an acoustic wave is traveling along a work bench has a wavelength of 3.33m what will its frequency be? Why do you suppose that is it easier for this type of wave to be travel through solid materials?

The frequency of the wave is 100Hz. I worked it out by doing the following:

v = fλ

f = v = 333  = 100Hz

      λ    3.33

Q4 Sketch a sine wave accurately of amplitude 10, frequency 20Hz. Your sketch should show two complete cycles of wave. What is the duration of one cycle? What is the relationship between the frequency and the duration of one cycle?

Here is shown two cycles of a sine wave with amplitude 10 and frequency 20Hz. The duration of one cycle is 1/20th of a second as the frequency tells us that 20 cycles will happen in 1 second therefore to find the period of one cycle you use the formula T = 1/f so T = 1/20.

Q5 Research the topic “Standing Waves”. Write a detailed note explaining the term and give an example of this that occurs in real life. (Where possible draw diagrams and describe what represent)

Standing(stationary) waves disturb but do not actually pass through the medium, it remains at a constant position. Stationary waves happen both in the air with sound waves and also in the ocean. If two waves collide because they are travelling towards each other the they cant go anywhere and become stationary.

Q6 What is meant by terms constructive and destructive interference?

Constructive interference is when two waves are happening at the same time but trough meets trough and peak meets peak. The two waves never touch but simply coexist.

Destructive interference is when the same two waves are not moving together and therefore trough meets peak and peak meets trough. The waves touch once a cycle and the resultant wave created by the two is a line.

Q7 What aspect of an acoustic wave determines its loudness?

The amplitude of an acoustic wave determines the loudness.

Q8 Why are decibels used in the measurement of relative loudness of acoustics waves?

Q9 How long does it take a short 1KHz pulse of sound to travel 20m verses a 10Hz pulse?

The time would be the same as the frequency of the sound does not effect the time taken to travel the same distance as speed remains constant at 333m/s.

Q10 Does sound travel under water? If so what effect does the water have?

Yes sound travels under water however it has a slower speed than in air so will take longer.

 

Digital Signal Processing Lecture

The Fundamental is the accumulation of all vibrations that merge together to create what is also known as the Basic tone. Other Vibrations however create a series of harmonic tones. The harmonic is a multiple of the fundamental tone(frequency) i.e. 2 x Fundamental, 3 x Fundamental.

The Amplitude of a sound wave is basically the height of half a wave, i.e. measured from the origin to the peak or trough. The higher/lower(or bigger/smaller) this is determines the level of the sound. For example, a wave with a high amplitude will strike the ear drum harder and therefore the sound is louder.
These measurements are hard to make and therefore sound is actually more often expressed in terms of Sound Level, measured in decibels.

All living creatures have and upper and a lower threshold of hearing which is the quietest or loudest a sound can be but also the frequency a sound can be to hear it. A humans threshold is different from other creature and therefore can hear different things.


Sound intensity = 10log10(Isound/IStandard) DB

The Inverse Square Law implies that the further you are from the source the quiter the sound is. Therefore a sound wave loses intensity over distance.
An echo however is the percieved copying of a sound due to reflection of the sound waves off of objects i.e. a tunnel. Time difference= (d1 + d2)/v
r(t) = s(t-d0/v)+alpha s(t-time dif)

Room reverb is similar to an echo with the exeption that it involves multiple reflections of the sound wave and the can all reflect back to the same point.

Sound Lecture

Transverse Wave - Ripple on the surface of the water and the ripples move from the disturbance in an outwards circular motion.

Longitudinal Wave - Vibrations move in parallel to the direction of the motion and also originate from the point of disturbance. Energy is passed between molecules leaving the first molecule in the same position i.e. newtons cradle.

Compression is a increase in the waves density.

Rarefraction is a decrease in the waves density.






Wavelength is calculated by the distance between two crests or troughs for a transverse waves and between two peak compressions for longitudinal waves.

The amplitude of a wave is its height from the origin to the peak of the wave i.e. half the height of a full wave.

Speed of sound - Metal   5000m/s
                         - Water  1500m/s
                         - Air   333m/s (350m/s??)

Frequency is defined as the number of waves to pass a point in 1 second and is measured in Hertz(Hz)

Velocity is defined as the speed at which the wave travels measured in metres per second(m/s)

Velocity = frequency x wavelength

Standing waves disturb but do not pass through the medium. violin strings vibrate with a node(minimum) at each end and an anti-node(maximum) in the middle. Note that nodes also occur in cavities such as a flute or a room. the nodes being in the walls and the anti-nodes being the middle of the room.