Golden Eyes: Experiments with Audio - Part 4 (I think I saw some noise!)

note: you can read part 1, part 2, and part 3.

Hi again,

In this part I will show another processing on our audio. Let's look at a kick drum waveform for the processed track D and compare it with our original:

Operation D

What do you see? Can you spot some difference? Perhaps if we could see the difference:

Whispering?

The difference is really minimum but there is definitely something there! This kick audio has some high frequencies in there and that makes it difficult to analyze. Below is a zoomed in part of the bass track and its processed version.

..or you have shaky hands!

Now it is easy to see that some low amplitude, high frequency and random looking data has been added in the processing. Here they are overlaid for comparison (click the image for a bigger version). Smooth red line is the original waveform while the blue jagged line riding on top of it is the modified one.

Overlay of process D

This type of effect is most probably some type of high frequency noise (or hissing) riding below our audio. Let's really amplify the difference track:

The portrait of a noise

Yes, it really looks like high-pass white noise here. In fact, I had put some high-passed noise generator plugin to get this effect.

What about when we listen? Well, the noise has been clearly heard and correctly identified as such when listened; especially when compared with the original audio. Many times some sort of tape hiss is deliberately added to tracks to get a more organic or vintage feel and it can be quite pleasant when used correctly. In fact many analog-mimicking VST plugins will just do that for the analog effect.

Hope you enjoyed that. In the next part, let's degrade the sound and see what happens!

Cagil

Continue with part 5.

Golden Eyes: Experiments with Audio - Part 3 (phase inversion, inverse phasination)

(It is recommended to read part 1 and part 2 beforehand.)

OK, let's subtract the clipped track from the original track to see only the differences. How do you subtract one audio from another? Well, you invert one of them and then 'sum' them!

Here is a small portion of our original vocal part:

 "eieieieieiiii" in about 50 ms

And here with the phase inverted version:

Like looking in the mirror!

In Cubase you can select the audio clip and apply Audio->Process->Phase Reverse to get the inverted version. Notice how it is inverted by the 0-dB-axis. Now, what if we play both at the same time? As you can guess, the answer is "complete silence" since the waves will superimpose and cancel each other completely! Let's bounce the summation result:

Silence...because, science! :)

So, in a way if A' is the phase inverted version of A, we confirm A + A' = 0. What about our clipped track in the previous part? Here another part from the vocal from the clipped track and compared with the original track:

Looks like digital clipping to me

Remember the 'shaving'? Now, let's see only the clipped parts by taking the difference (summing with the inversion of the original):

Ahh, so this is the place where all those clipped data was going after all!

Now we can clearly see what exactly is being clipped in track C. Notice that the weird bounce-back dips we have talked about in the previous part are also clearly present in the difference. Pretty neat, don't you think? In the next part, I will investigate an interesting 'process' on the original.

Continue with part 4.

Cagil

Golden Eyes: Experiments with Audio - Part 2 (are you shaved?)

Continuing from the Part 1, let's look at the waveform for track C:

Track C

If you are familiar with waveforms, you may recognize the apparent shaved-ness of the data here. I have to point out that all of the processes/artifacts has been applied to each instrument part separately and then they are glued together. Because of that, the flatness is at different amplitudes for each part as can be seen above. If we zoom into the orchestra part, it is obvious that the flat shaving is amplitude dependent and the quiet parts are not affected:

Orchestra part

Let's compare it with the original (select both audio clips in Cubase and then select 'events to part' from the Audio menu then press Enter):

Comparison of the orchestra part

Now the effect is clear! Remember to compare the left channels and right channels with each other. There are two main ways to do this effect to an audio: 1) clipping 2) limiting/maximizing. Of course clipping can also be considered as a crude type of limiting/maximizing. In clipping, the digital audio signal has become above the maximum representation capacity of the digital audio format and become cut-off abruptly. In limiting/maximizing, the audio has been similarly prevented to go above some limit but the transition to the cut-off is more gentle to prevent audio artifacts and degeneration. To make it clear, clipping is 'bad' and you don't want it to happen unless going for that specific effect. On the other hand limiting (which is a form of compression) and maximization are very common processes in the audio world but their specific usage is outside the scope of this post.

So, which has been applied here? We need to zoom in further:

Zoomed in to orchestra part

...and further:

I see waves itself!

..and further:

Shaving in plain sight

Now we see the individual waves and it looks like digital clipping more and more. If we zoom in further in the audio part editor in Cubase, the display changes to lines:

Really zoomed in

Here, the cut-off parts look flat with some exceptions. For a sound wave flatness is usually audible as pops and clicks if separated out in time, but if they are really frequent in a small time period (as in here, look at the timecode) then it sounds cracked and unpleasantly distorted (clipping distortion). (If you remember that sound is essentially a continuous or smooth change of air pressure as a function of time, the musical content will be essentially removed from these flat parts).

Even further...

I produced this effect by turning up the volume fader of the main output in Cubase allowing it to clip and then bouncing the result into the project. Let's overlay the differences showing the clipping line:

Overlay of the effect

It is interesting that the clipped parts are not actually completely flat as expected; but instead almost dips or bounces back as the clipped data goes higher. It is really weird and if anyone knows why this is happening please share it in the comments. I think this may be the result of how Cubase or my audio interface are handling the clipping data.

As another example, let's look at the drum kick clipping. Here the longer wavelength low frequency part of the kick drives the data over the clipping point. Since the higher frequencies 'live' on the lower frequency waveform, they are also gone forever (apart from that interesting dipping effect).

Overlay of the effect in the drum kick

This will provide a reference point when we compare the results with the more gentle maximizing and compression effects. In the next part I will look into phase inversion and difference of two tracks which will come really handy for our analysis.

Take care until then,
Cagil

Continue with Part 3

Golden Eyes: Experiments with Audio..uhm... part 1!

Hello everybody,

I am starting a new series of mini articles/musings under the title: "Golden Eyes". It is derived from "Golden Ears" which is a comprehensive free hearing/listening test by Philips and I strongly recommend you to take it if you record, mix any music or you are an audiophile. As of now, 1798 people completed the last level. It begins simple but becomes incrementally difficult as you approach to the latest sections and I was literally trying to hold on to the fringe of my hearing to finish it :).

Golden Ears Quiz Last Level

I have been tutoring about recording, audio engineering, mixing, and physics of audio for a while. During those sessions I have come up with my version of Golden Ears as a fun quiz for my students. I cut out some sections of instrument tracks from one of my mixing projects and then applied various effects and artifacts/distortions on it and then bounced the results on separate tracks. Then, I asked the students to identify the process involved for each track.

A Fine Selection of Vintage Waveforms!

It was tons of fun to watch their reasoning and descriptions of the effects/artifacts they hear or see. Sometimes they tried to identify the process just by listening, and sometimes by doing A/B comparisons with the original recording. But other times they were identifying the process just by looking at the waveform and/or comparing it without any listening involved. Another approach we have tried is to subtract the original from the altered tracks and listen/see the differences only (that proved to be reeaaally helpful). So that gave me the idea of Golden Eyes and hence this post (the tracks used are copyrighted anyway, so doing this without any sound upload is also highly practical :D).

Let The Games Begin!

I won't be giving out the list of processes applied beforehand since trying to guess is part of the game! Another reason for writing about this is that I am introduced to the captivating glitch art / databending world by a friend of mine and as a start I want to explore applying audio processing on other types of data to create art (or world domination haha!).

Till next time,
Cagil

Continue with part 2 here!