[Simon]

You can use the terminal feature on Edina, then follow these instructions as if you were updating on your own machine, but using the terminal on Edina (in a browser).

There are instructions on using the terminal in Edina in the sp-m0-how-to-start notebook (look for the heading “Alternative: Using the Noteable terminal”).

There are more tips on using Edina Noteable in their user guide.

[Simon]

First, try rebooting the Virtual Machine.

Some other possible ways to diagnose the problem:

1. can you reach websites (e.g., http://www.ed.ac.uk or google.com) using Firefox in the VM?

2. are you in University accommodation (in which case you don’t need the VPN – you are already inside the University network)?

3. use a browser on your personal computer, and also in the VM, and type “what is my ip” into the Google search box

[Simon]

The $ indicates the shell prompt – the command to run is the part after it.

[Simon]

Looks like you are trying to install the VPN inside the Virtual Machine. That’s not the way to do it. Install the VPN on your personal computer.

To use the VPN with the Virtual Machine (e.g., for copying the files needed for the first assignment), connect to the VPN on your personal computer, then start the Virtual Machine. The Virtual Machine uses your personal computers network connection, so will also be using the VPN.

[Simon]

Thanks for testing. Those errors should not matter. Did you see rsync copying a lot of files the first time you ran it?

The second time you run rsync it won’t copy anything that is already copied, so it runs really fast.

Please try it one more time. You will always get the “Could not chdir…” error – ignore that. The other error “…failed to open…” should now be solved.

[Simon]

That’s a philosophical question, to which I have no answer. But I do have an engineer’s answer:

We have a toolbox. Our tools are techniques like short-term analysis, the Fourier transform, IIR filters, etc.

In any toolbox, there are usually several tools that could do the job. You could hit a nail with a spanner, but you’d be a bad engineer and the nail probably would not go in straight!

Being a good engineer usually means selecting the best tool for the job at hand, and having the skill to use it correctly. Almost all the time we select a reliable, tried-and-tested tool. One that we (and many other engineers before us) have used before, and that we understand. It will have limitations, but we know what they are and can live with them.

Very rarely, none of our tools will do the job, and so we need to invent a new tool.

[Simon]

I’ve created a forum for reporting errors in the Jupyter notebooks.

Most readings have a forum already which is where to report errors or ask for clarification.

For anything else, just post on any forum and we’ll see your message.

[Simon]

Please try the machine scp1.ppls.ed.ac.uk and report back (instructions now updated).

[Simon]

Please try the machine scp1.ppls.ed.ac.uk and report back (instructions now updated).

[Simon]

No, that’s not correct. The last N/2 values are identical to the first N/2 – they are just copies of the same values (their ordering is mirrored around the Nyquist frequency).

There are only N/2 magnitudes. No more.

The N numbers (samples) in the time domain (waveform) have been transformed into N/2 magnitudes and N/2 phases in the frequency domain. So, in the frequency domain (= magnitude spectrum & phase spectrum) there are also exactly N numbers.

In other words, the transform to the frequency domain has preserved all of the information in the waveform. That means the inverse transform will perfectly reconstruct the waveform.

[Simon]

Yes, that’s all correct.

[Simon]

You obtained the notebooks from a git repository and that created a folder called uoe_speech_processing_course somewhere on your machine.

Navigate to that folder in the terminal before running jupyter notebook and then your browser will open in the right place.

Otherwise, just navigate in your browser to wherever you have uoe_speech_processing_course (but noting that Jupyter won’t allow you to navigate upwards from the folder it was started in – this might be your problem?).

[Simon]

It’s really not easy to look at a waveform and guess how much energy it will have at each harmonic (except in some special cases like the above). That’s why we prefer to inspect signals in the frequency domain.

Sounds like you are spending too much time looking at waveforms and not enough time with the spectrum?

Periodic signals

All periodic signals have energy only at multiples of the fundamental frequency (which are called the harmonics). We can see the periodicity in the waveform, but not much else.

How much energy at each harmonic is what differentiates one signal from another.

Special cases (where inspecting the waveform makes sense)

The sine wave is the simplest case: it has energy at the fundamental frequency only and no energy at all the other multiples.

The impulse train has an equal amount of energy at every multiple of the fundamental.

A square wave has energy at all the odd multiples of the fundamental and no energy at the even multiples.

The general case (where inspecting the waveform is of limited use)

Voiced speech has energy at all multiples of the fundamental (in common with the impulse train) but the amount of energy varies with frequency (why?) and so voiced speech does not sound like an impulse train.

[Simon]

Yes, the figure is different in the 2nd edition (the attachment in #7813 is from one version of that edition but this has serious errors in it), in which there are 4 sub-plots all with the same spectral envelope but different F0.

In the top sub-figure, the waveform makes 6 cycles within the first pitch period and that’s what the “6 peaks” is referring to. This is the resonance of the vocal tract – the “ringing” of the filter in response to an input impulse. It corresponds to the peak in the spectral envelope at 600 Hz.

All the waveforms in the other sub-figures have the same ‘ringing’ behaviour, it’s just that the input impulses are spaced at different fundamental periods.

Attached is a correct Figure 4.13 from my hardcopy 2nd edition.

Attachments:

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[Simon]

The course deliberately uses multiple modes of learning so you see material from many points of view. You’re right that the SIGNALS notebooks were a bit tough – that’s because we wanted you to see the mathematical way to do signal processing, because eventually you will understand some of this and see that it can be the most simple and direct route to understanding. For now, just getting some intuitive understanding is all you need.

The gap between the videos (pretty pictures but glossing over details) and the notebooks (all the gory details, possibly too much) can be filled by some of the readings and by asking questions in tutorials or here on the forums. Try posting about what you think you understand and ask for confirmation, as well as posting about what you are struggling with.

In Module 3, there is a consolidation tutorial for the SIGNALS material – use that to ask questions about how much you are expected to understand at this point in the course (and how much more by the end of the course).

I hope you are writing your own notes, as you would if we had lectures. Writing your own ‘textbook’ which draws together all the material is my top tip for learning on this course.

Persevere for a week or so, then tell us how you are doing.

[Author]

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