A really good video I have found on youtube. it simplifies waves and presents them really well.

waves

Week 4- Editing sound files

I have previously altered audio files with acid pro and audacity in high school, but this is my first time using Adobe Soundbooth CS4

Original File (Left) and file after Distortion (Right)

Distortion made the soundtrack sound like it was a heavy metal track.

 Original File (Left) and file after Phaser (Right)

The Phaser seemed to add a strange synthetic sound to the audio, gave it an outer space feel.

Week 4- Lab

After compressing multiple audio samples it seems that the compression lowers the amplitude of the audio wave. The peaks of the wave are affected differently, so that the ‘loudness’ of the audio is level where the human ear will not recognize much change in the amplitude once the compression has been applied.

This also applies to the ‘quiet’ sounds, making the sample louder where we will not hear much variant. This would be used in technology such as CD’s where we have large audio files and a very limited amount of storage.

Compression is also really useful to prevent clipping. Clipping is when an amplifier is pushed too far and attempts to output a voltage out with its capacity and you get an almost buzzing sound.  Compressing the audio file helps reduce the clipping because it reduces the amplitude where clipping may be a problem.

The effects of compression in Soundbooth. The first and last words in the audio file are compressed and the middle wave has not been altered.

Q. Is speech a musical sound?

A. Yes as we all have different bass and treble in our voice, we can alter our voice to sing to where we perceive musical but speech in itself has musical qualities that we use in everyday life but do not notice.

The effects of Reverberation in Soundbooth. The left image is the original, the right has reverberation applied.

Reverberation in enclosed spaces is created by reflections from surrounding walls arriving within short periods of time, for example shouting into a cave, the sound comes back relatively clearly and does not differ in amplitude.

Digital reverb is added by passing the audio signal through a “feedback delay circuit” which creates an echoing effect.

The first test made the signal sound like it had been recorded with a subpar microphone and the second (adding the roller-disco preset) made it sound like it had been recorded underwater.

Week 3- the human ear

The Outer Ear
The outside of the ear, the pinna and the ear canal act as a tunnel, making the vibrations of a sound wave travel to the ear drum which in turn vibrates. this vibration amplifies the sound so that we can process the sound. the pinna also allows us to percieve the direction of the sound source. 

The Middle Ear
The vibration of the eardrum is transferred through the chain of small bones, the ossicles, which then vibrates the oval window of the cochlea.  this chain helps to make up for the lost energy when the vibrations travel through air. this then goes through the fluid in the cochlea.

The Inner Ear
Vibration of the oval window produces pressure waves in the cochlear fluid that stimulate the cochlea. Sensor cells within the cochlea cause neurons connected to our brains percieve this. They transmit timing, amplitude and frequency information to the hearing part of our brain.

Human Hearing and Speech
Human hearing covers a range of frequencies from around 20 Hz to 20 kHz and responds to a huge range of sound levels.

in this range are frequencies and levels generated by speech.
The lowest sound pressure level (SPL) that humans can hear varies with frequency and is called the Hearing Threshold.
the best sensitivity is normally in the frequency range of 1 kHz to 4 kHz.

MPEG/MP3 Audio Coding
The use of MP3 of a lossy compression algorithm is designed to reduce the amount of data required to represent the audio recording and still sound like the original soundtrack. A MP3 file that is created using 128 kbit/s will result in a file that is 11 times smaller than the CD file created from the original audio. A MP3 file can also be constructed at higher or lower bit rates, with higher or lower resulting in a difference in quality.
The compression works by reducing accuracy of waves that are considered to be beyond the hearing ability of most people. This method is referred to as 'perceptual coding'.

Week 2- Getting familiar with waves

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

λ=v/f
λ= 340/1000
λ= 0.34m
λ=34cm



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?

freq. of note at orchestral  A = 440 Hz

T=1/f
T=1/440
T=0.0027

Q3 If an acoustic wave is travelling 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 if wave to be travel through solid materials?

f=v/λ
f=4000/3.33
f=1201.2 Hz

the molecules in a solid are more tightly compact

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?

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)



A Standing Wave is a wave form that does not seem to travel. They are caused by two waves moving in opposite directions with the same amplitude and frequency, causing interference. The string has two points, a maximum and minimum, the maximum is called an anti-node and the minimum, a node.

When the two waves collide they combine to form a Standing Wave.

An example of a standing wave would be in a Guitar or Violin. The two points of the string are fixed (the nut and bridge) and therefore the waves cannot ‘travel’ and hence a standing wave occurs.

Q6 What is meant by terms constructive and destructive interference?

interference is when two waves meet, constructive interference is when the two waves are 'in phase' (the peaks and troughs are the same). When the interference is constructive, the amplitude increases, making the signal stronger. For Destructive interference is the exact opposite, the waves are not in phase and the amplitude decreases, making the signal weaker.
Q7 What aspect of an acoustic wave determines its loudness?

The amplitude

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

Decibels are used because it is a logarithmic measurement that reflects the range of sound intensity our ears can hear and how we perceive loudness

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

It would take the same amount time.

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

Yes, it speeds the sound up to 1500 m/s

Week 1-Lecture

Sound

Sound is a phenomenon that stimulates the ear.

Waves

Sound travels in waves through a medium such as a solid, liquid or gas.

Two basic waves are transverse and longitudinal

Transverse Waves

An example of a transverse wave is a rippling effect on water.

The waves are straight up and down from the line along which the wave is travelling

Longitudinal waves

An example of a longlitudinal wave is a slinky.

The waves push back and forward and hit neighbour molicules to transfer the energy of the wave.

The molicules do not move much once the energy has passed through them

Compression and Rarefaction

Compression is the increase in density

Rarefaction is the decrease in density

This is what waves are made up of.

Wavelength, Velocity and Amplitude

Wavelength is the distance between a point in a wave that occurs more than once e.g. the start of a wave and when it repeats itself

Wavelength is measured on metres (m)

Velocity is the speed of the wave.

In steel a wave travels just under 5000 m/s

In water a wave travels around 1500 m/s

In air it travels around 333 m/s

Velocity is measured in metres per second (m/s)

Amplitude is the perceived ‘loudness’ of a wave

Amplitude is measured in metres (m)

Frequency is the number of vibrations per second is in a wave

Frequency is measured in Hertz (Hz)

This leads us on to the equation

 v=fx λ

Standing Waves

Standing waves are stationary waves

They disturb a medium but do not travel through them

An example of this is a guitar string.

These waves have a node (min) and an anti-node (max)