Golden Eyes: Experiments with Audio - Part 5 (a 'bit' of degradation)

[ Catch up: part 1, part 2, part 3, part 4. ]

Welcome back!

Alright, just look at this mysterious process 'H' in comparison with the original track for a minute. Here it might help to have high frequencies. Therefore I chose a single cymbal hit part of the track.

Sneaky process H

Can you see a difference (you can click all the images to enlarge them)? Probably not. Amplitudes and overall form looks to be the same. Let's see the difference of those:

Silence?

Ok, looks completely silent! Maybe they are identical. What if we listen to the tracks?

{...a quick listening later... well, this is Golden Eyes, no eavesdropping! ;D }

Crazy! There is definitely something big lurking in the audio. The cymbal sound is much much more 'hissy' and also there are some loud digital/robotic distortions. It seems that the quieter the audio the more pronounced these robotic effects. Since the tail (release) part of musical audio is usually a gradual amplitude decline, it is really audible in those tail parts. For example during the synth solo we hear some distortion along with a loud hissing; but at the tail part of the solo there is a long gradual decline of volume and at this part it is really glitchy, almost like a science fiction sound effect. I will show that part in a minute.

Turning back to the cymbal sound, here is the amped-up (amplitude exaggerated) version of it:

What is there?!

Now we see that there is some data in the difference. Let's zoom into the beginning of that cymbal attack:

Nope...

The applied process is now somewhat visible to the trained eye but let's make it clear (enhance!) [the amping-up is done using the vertical slider in Cubase visible on the upper right side of the image below]. We both zoomed and amped-up here. The waveform in the window takes about 2 milliseconds:

If I reaally squint my eyesss...

Could you notice the processing yet? What about if we overlay them:

OK, red one is the lazy one.

The red one is the process track. It looks like it skips some values and rounds them up or down (hint hint!). I think we should look at the quieter tail part of this cymbal sample and reeeeally amp it up to see this rounding in action. Here is the tail part of the cymbal waveform:

Cymbal tail comparison

Bingo! Track H looks like a poor copy of the original trying to imitate but failing miserably :P. It is now clear that the values are restricted and being rounded in the processed track. It also looks like the minimum value change time is longer (the sample rate is lower). But it is just an illusion when the value does not change from one sample point to another because of the rounding restriction. Just look at the quick change of values in the left channel of H visible in several places. So, the sample rate looks to be the same, but the number of distinct values the data can store is reduced!

This is called the bit depth of the audio sample. In the original track bit depth is 24-bits which means there are 2²⁴ (or over 1.6 million!) distinct values to store the current amplitude of sound at the sample point. In the modified track bit depth has been reduced to only 8-bits (think Atari) which corresponds to 2⁸ or 256 distinct values. So, for every two adjacent possible values in the modified track, there can be 65536 possible distinct values in the original one; and the 8-bit version had to round these to the nearest one of the 256 values.

This illustration shows the difference as bit-depth doubles up (original audio is a sinusodial wave):

Let's see an overlay of our example to get a better look:

Bit-depth difference is in the house!

Since the changes in the audio now more rectangular and less sinusodial, the sound produced by the speakers become distorted. This almost looks like the chiptunes or 8-bit music of the past. However there are some differences since Cubase extrapolates this to project bit depth (24-bits) and our audio interface is also set to 24-bits. Also our sample rate is still at 48kHz; way higher than the tunes of the digital past :).

If you want to export some audio with a different bit depth, you can choose the desired bit depth in the export dialog as shown below. However it will be up-bit-depthed (is that a thing?) to the project settings when you import again.

Cubase export dialog

Finally, as promised, the tail of the synth solo where it sounds almost like an android (notice the amp-up factor):

I, robot!

Till next time,

Cagil

Continue with the part 6.