Week 3: 12/10/2012

Lecture  

Note for blog readers: I would type out a lot more in my own words, but when there is a picture on the PowerPoint lecture slide, I just put the who slide in the blog because the whole slide is a picture all in its own right, not a slide with words and a picture.  

Today we were taught about Digital Signal Processing.  This involved learning about digital and analogue signals in respect to sound waves.

The information that the PowerPoint taught us all is on what happens when sound is received from a device (such as a microphone) and then processed by the main device the receiver is connected to.  An image was used to represent this by showing what happens on the analogue and digital sides of a typical digital signal processing system.  (See figure 1)

Figure 1 - A Typical Signal Processing System  

We also learned the basic things needed in the system are input and output filtering, analogue to digital, and digital to analogue conversion and a digital processing unit.
Respectively, these are needed because without input and output, you would not be able to pass in sound or receive it; the system would not be able to process an analogue signal (as digital is 1's and 0's i.e. use of the binary system to show voltage's and other properties of waves) and would not be able to produce an output, as we understand the analogue wave (that is, we perceive it) and the digital processing unit processes the digital signal to understand the sound and all of its properties such as filter, pitch warp, echo etc.

The next part of the PowerPoint presentation went on to explain why we would use digital processing.  The three main reasons are: precision, robustness and flexibility.
Precision isn't really described or explained in terms of why it is needed, but what is explained are the factors that can affect the precision of the sound wave and the digital signal processing sequence in relation to it.  (See figure 2)
The robustness of digital systems is shown mostly by the advantages it has over an analogue system.  These advantages are the digital systems are inherently less susceptible than analogue systems to electrical noise (pick-up) and component tolerance variations.  (See figure 3)
The flexibility of digital systems allow easy programmability which in turns allows upgrading and expansion of the processing operations.  This can be done without necessarily incurring large scale hardware changes.
Practical systems with desired time varying and/or adaptive characteristics can be constructed.
(See figure 4)

Figure 2 - Precision  

Figure 3 - Robustness  

Figure 4 - Flexibility  

To accomplish all this, a sound card that is functional must be present and being used.  (See figure 5)  

Figure 5 - Simple Sound Card Architecture  

When sampling a sound, the system will take a point at nT seconds where it shall begin sampling and then it will use one full period per sample.  The sampling rate is usually the double of the frequency of the human hearing range.  (See figures 6 and 7)  

Figure 6 - Sampling a Signal  

Figure 7 - Sound Card Sampling Rates  

Most modern sound cards support a 16 bit word length coding of the quantised sample values.  This allows a representation of 2^16 (65536) different signal levels within the input voltage range of the card.
(See figures 8, 9, 10, 11 and 12)  

Figure 8 - Quantising the Signal Amplitude  

Figure 9 - Coding the Quantised Amplitudes  

Figure 10 - Sound Card Word Length  

Figure 11 - Comparison of Audio Recording Specifications  

Figure 12 - Dynamic Range  

Lab  

In today's lab session we undertook a mock test of the information we learnt from the first PowerPoint.  Quite a few of the questions caught me off-guard.  I am just hoping that I have not failed and I am only doubting myself because it was a test and I do not yet know the outcome.  I find that I doubt myself quite a lot.  But then, if I don't get my hopes up, then I can't be disappointed.

I then done this blog as well as slightly edited another.  Shall edit the others more thoroughly however, in my free time.