Week 4: Audio Lab 2

Week 4: Audio Lab 2

1.      Run Audacity. Select Tracks-> Add New-> Audio Track which as you can see has defaults setting of MONO, Sampling Rate 44100Hz, 32 bit float. Click on the inverted triangle on the audio track to change the setting to 16 bit PCM What do each of these setting mean? (Research , discuss with your tutor and answer in your note)
MONO is single channel sound reproduction. This means that there is typically only one speaker, microphone or channels that are fed from a common signal path.
Sampling Rate is the conversion of a sound wave to a sequence of samples. A sample being a set of values linked into the sound wave.
PCM or Pulse Code Modulation is a method in which audio is converted into binary numbers, be it 16 or 24 bits or 32 bit float. By converting the audio into binary it can be represented digitally and then back into audio. Using PCM the waveform is measured at evenly spaced intervals and then amplitude is also noted for each of these measurements.

2.      Use Audacity Help at any time.

3.      Use the Generate->Tone option to generate 1 second of a sinusoid (single pure tone) of frequency 440 Hz at  amplitude 1, mono, 16bit, sample rate (frequency) 44100 kHz. Save the pure tone as a *.wav file in C:\TEMP or on your pen drive if you have one.

4.      By using the same option, create similar tracks for each of the harmonics up to and including the 9^th in the proportions shown below. Add the fundamental and each of the harmonics to each other by selecting all waves (CTRL A) and pressing CTRL SHIFT M. Sketch or cut and paste the result into your lab document and describe what you see.

Harmonic Number	1	2	3	4	5	6	7	8	9
Amplitude relative to Fundamental Let it be x	1	0	1/3	0	1/5	0	1/7	0	1/9
Amplitude in dB 20 log x	0	0	-9.54	0	-13.98	0	-16.90	0	-19.10

Above are five screen captures of generated tones in audacity. The first of the five is the track for the fundamental. The next four are the fundamental being merged with first the third harmonic, then the third and fifth and so on and so fourth. As the harmonics for each track increase the wavelength decreases and the amplitude for each track also decreases. The general shape of the waveform is moving towards square in style but more so when all five are merged together. The first track is quite deep in sound. The second is a higher pitch and this trend continues. The merge track however shares most similarities with the first track (1st harmonic/100Hz). From this I can tell that the smaller wavelength means a higher pitch for the sound and the amplitude of each track obviously determines the volume.

5.      What shape is the waveform gradually approaching? Listen to the wave as you add more harmonics. Does the timbre change?

See Above.

6.      Similarly to the previous lab view the frequency content (Magnitude Spectrum) of the waveform using the Analyse->Plot Spectrum option. Compare the peaks in this display with the fundamental and the harmonics you have added to it. Sketch or cut and paste the spectrum in your lab note and describe it.

     The first image is the Freqency Analysis of the Fundamental in this case. The second image is of the fundamental and the third harmonic, the third is the fundamental plus the third and fifth and so on and so fourth again. As you can see with the addition of each harmonic the peak for each harmonic is lower than that of the previous harmonic or fundamental. The Fundamental hits 0dB and 2000Hz. The merge of the fundamental and third harmonic hits almost 3000Hz and just below -12dB for the harmonic. This pattern continues throughout the images. 

7.      Now view the Spectrogram of the waveform using the audio track triangle and selecting spectrum setting. Describe and sketch this result in your note. Save the final waveform as a *.wav file in C:\TEMP. Listen to the waveform and compare it with the sound of the original pure tone sinusoid.

Spectogram shows intensity by colour or brightness on the axis of frequency and time. The mixed track has a much higher pitch than the original pure tone. As you can see below the amplitude is displayed in the blue colour meaning that it is much less intense as the harmonics are added to the mix. Each track can be seen seperatly in the mixes in the form of the bright white lines meaning that their much more intense. The frequency also climbs as the harmonics are added as you can see the left axis for the first image says 0K and the final mix hits a high of 5K.

8.      Now start afresh and add to the Fundamental pure tone the harmonics up to and including the 5^th in the proportions shown below. Display and sketch the waveform each time you add another harmonic.

Harmonic Number	1	2	3	4	5
Amplitude relative to Fundamental x	1	1/2	1/3	1/4	1/5
20 log x	0	-6.02	-9.54	-12.04	-13.98

9.      What shape is the waveform gradually approaching?

As you can see from the above pictures. As you add the harmonics to the fundamental it slowly gains a sawtooth shapes and starts to become a sawtooth wave.

10.  View the frequency content (Magnitude Spectrum) of the waveform as previously. Identify the peaks in this display with the fundamental and the harmonics you have added to it. Sketch it in your lab note.

       The first image here is the fundamental again. The exact same as before. The following images are the merging of the 2nd, 3rd, 4th and 5th harmonics to the wave. Once again you see the same pattern. Each time a harmonic is added it's peak is lower than the one to it's left. A higher frequency occurred in the merger for the first set of harmonics as opposed to this set. A higher dB was also reached in the first set with this set not hitting above -18dB.

11.    Save the final waveform as a *.wav file in C:\TEMP. Listen to the waveform and compare it with the sound of the pure tone, and the previous waveform.

The pure tone is still a medium volume lower all round pitch sound. The Square wave is a much louder higher pitched sound due to the multiple amplitudes from the added harmonics. The Sawtooth wave is a similar volume to the Square Wave but it has a lower pitch.

Noise, Mixing, Signal-to-noise ratio, and Filtering 

1.      Open the waveform noise1.wav  This is a white noise file. Listen to this nuisance file. View and sketch this waveform in the time domain and in the frequency domain.

2.      Add a sinusoid of amplitude 0.02, 1kHz frequency of 1s duration. Does the resulting waveform look sinusoidal? How does it sound? How does it look in the frequency domain?

The resulting tone does indeed appear to be a sine wave, it does look sinusoidal. The White Noise track however does not look sinusoidal. The tone peaks at below -18dB and peaks at 1000Hz. The tone like before is a high pitched ring, quieter than the others though.

3.      View and sketch the spectrum, view the spectrogram, and listen to the waveform. Locate the pure tone if possible. Save the mixed waveform as an *.wav file in C:\TEMP.

You can visibly spot the peak of the tone among the white noise in the frequency domain. (The peak at 1000Hz).

4.      Try using the Effect Graphic Equaliser options of Audacity to select the tone and reject the noisy in the waveform( we need a slider at max at 1000KHz and sliders at zero elsewhere if possible). Does the waveform look more sinusoidal than before? If so is the period of the waveform approaching that of the original pure tone? How does it sound? To what extent did this filtering work?

As you can see above the resulting waveform following the equalization is getting closer to being sinusoidal. A comparison is shown with this waveform and that of the original pure tone, only more zoomed in. The White Noise is no longer quite as prominent but still very much there. To some extent I would say that this filtering has worked.

5.      On waveforms of your choice from freesound.org  explore the effect of the other filter options that are available.

Here you can see the original track, a line from the Austin Powers movie and below it the same track with several filters. I have used a fade in and out effect to bring down the volume at a  steady pace for the end of the track and to do the same in reverse for the start. The echo as you can see has kept out any breaks in the waveform as the sound continues to play through these parts. Most notably in the middle where Austin takes a break in his dialogue,