
Reverberations: An 8-bit approach to J.S. Bach - 8bitsrule
https://www.linusakesson.net/music/reverberations/
======
zw123456
This post reminded me of my Senior year of EE, we were supposed to do a senior
project and I decided I wanted to make a custom IC to play music (our
University has a chip fab facility). Keep in mind this was 1978 so the size of
the chip was goin to be limited given our facility. I did not know a lot about
music, I knew I liked music but I just didn't know a lot about the theory
behind it. So I decided to take a music class as an elective. After I enrolled
in the class I was told by fellow students that this class was "an easy A". I
was tempted to drop the class because I was not looking for an easy A I was
looking to learn about music. On the first day of the course the professor was
an older, grey haired older gentleman. He explained that the course would be
composed of some music theory and some listening. We were to go to listening
rooms and listen to various pieces of classical music and become familiar
enough with the music to be able to identify it when hearing it. Again, it was
1978 so the music rooms contained vinyl records and record players and
headphones. Our first Quiz came and the professor played various records and
we were to identify each piece. To my surprise and amazement the other
students were able to easily identify each piece. I was not able to pick out
even one. The music theory part I was picking up easily but the listening part
I was struggling with. I spoke with the professor and explained to him what my
project was and he seemed very interested. We got into a long discussion about
it which I was really excited about that he was so interested in what I was
doing. I explained to him that part of my dilemma was to fit the notes into a
small amount of memory that I would be able to fit into the chip I was making.
He suggested that I look into Bach, specifically Fugues because there was a
lot of repetition, sometimes the same notes simply shifted in tone etc. That
was excellent advice. I continued listening, more and more time in the
listening rooms but for some reason I was just not picking up on how to
identify the music as easily as the other students in the class. I finally
asked a fellow student how he was able to do it so easily. He said that
everyone in the class had notes that he showed me, the notes said things like
"blue label with yellow writing", "red label, blue writing" and other such
things relating to the appearance of the labels on the records. Again, it was
1978, and the professor would hold up the record to the light, then place it
on the turn table before playing each piece, the other students would then
refer to their notes which they had prepared in the listening room. They were
cheating. I really liked this professor who I had forged a relationship with
so I went to him and explained to him what was going on and that people had
told me his class was an easy A. He thanked me and asked how my project was
going and we talked about that. He didn't seem mad or perturbed particularly.
He mentioned that he would appreciate if I brought my project by and show it
to him when I finished it and I said I would. The final exam day came and I
had continued the listening sessions and had decided not to cheat like
everyone else, I really wanted to learn about music. I was really glad I made
that decision because for the final there was a written theory portion and a
listening and identifying part. The professor brought out a tape deck (reel to
reel) and would start and stop it for each piece or portion of a piece we were
to identify. You could hear the air go out of everyone's lungs in the class
(except me). I got a little smile and proceeded to identify each piece to my
own surprise. Later after I had presented my project to my EE professors (and
got an A for it) I took it to my music professor and showed it to him, he
really liked it, I had hard coded Toccata Fugue in D-minor. He revealed to me
that I was the only one in the class that passed (I got a Not so easy but
satisfying A). He flunked everyone but me ! I kinda felt bad about that for
about one minute.

~~~
pjc50
Thanks for the excellent story. Doing your own music player chip as an
undergraduate in 1978 is no small achievement.

> He said that everyone in the class had notes that he showed me, the notes
> said things like "blue label with yellow writing", "red label, blue writing"
> and other such things relating to the appearance of the labels on the
> records

This is a classic mishap for machine learning systems as well, picking up an
unintentional but clear "sideband" channel.

~~~
jerf
A classic mishap for human learning as well. I minored in music, at what
wouldn't even be a particularly prestigious music school or anything. I am
sure that had the music students not cheated in the first place, they'd still
have found it easy to identify the pieces. Assuming the professor was drawing
from the canon, a good chunk of them should already have known a number of
them. But they took the easy path, for something that should already have been
pretty easy....

(The theory is what they should have been having trouble with. The musicians,
in general, _hated_ theory class. It was exactly the sort of thing they'd
generally tried to get away from by going into music. This is almost a quote
from them. Exceptions exist, of course, but generally they were not enthused.)

------
ciconia
> If so, how come a church organ doesn't sound like a chip tune, which is also
> built up from simple waveforms? Well, actually it will, if you remove the
> church.

That's not true. In the real world an acoustic device will never generate a
pure sound. An organ pipe will generate all sorts of artifact noises and its
overall sonic behaviour will be affected by temperature, humidity, barometric
pressure, and its physical promixity to other pipes (interference is a common
problem in mixtures).

It is important to note that organ builders will graduate the different pipe
dimensions within a single register in order to achieve a homogeneous sound
from low to high notes, but that graduation does not necessarily follow
physical laws but rather an approximation. Sometimes the graduation will
involve jumps or repetition in order to create a register with a mixed
character.

Finally, the voicing of individual pipes, done by hand, will (when done by a
master voicer) balance character and homogeneity. Each register will have its
own personality, but each note will sound slightly different.

> You have to add movement, energy, and emphasis (which, on an organ, has to
> be implemented by varying the duration of the notes, and the pauses between
> them, because there's no dynamic response).

On mechanical organs, a good player will also be able to adjust the opening
and closing of individual pallets (valves) using their fingers, in order to
control the attack and decay of individual notes.

~~~
mrob
An organ pipe, when played on low to moderate pressure and allowed to reach a
steady state, generates a pure harmonic tone. There is only a single audible
oscillator (either the column of air in the flue pipe, or the acoustically
coupled system of the beating reed and the column of air in a reed pipe), and
this oscillator is periodic, so all partials are exact integer multiple of the
fundamental.

This is not true of all instruments. A string oscillates both by tension along
the string and by bending across the string. The bending component becomes
especially important with thick strings, so a bass guitar produces noticeably
inharmonic sounds. This can make the sound more complex and interesting, but
it can also result in "muddy" sounding chords. A hammered string, such as used
in a piano, works the same way. Pianos traditionally compensate for this by
using "stretched" tuning, i.e. going up an octave is slightly more than a
doubling of a frequency. This helps the harmonics of the chords line up with
the slightly sharp partials of the inharmonic tone.

Another way to avoid the inharmonicity is with bowed strings. Here the slip-
stick motion of the bow resets the motion of the string every cycle, like hard
sync in a chiptune. The bowed string in steady state is purely harmonic.

Tuned percussion instruments have even more oscillators interacting. A marimba
bar twists and stretches along many different axis, resulting in a complex
inharmonic tone. A skilled tuner can adjust the shape of the bar to bring many
of the partials close to integer ratios. The same is true of bells.

See
[https://en.wikipedia.org/wiki/Inharmonicity](https://en.wikipedia.org/wiki/Inharmonicity)

A pipe organ can have a noisy "chiff" at the start of the note, but whether or
not this is audible depends on how the pipes are voiced. It has been
considered desirable or an unacceptable fault according to the fashions of the
time, so there is nothing wrong with omitting it.

It is not practical to control how far the pallets are opened by partially
depressing the keys. In a mechanical action organ it takes significant force
to overcome the initial air pressure, which generally makes the pallet spring
all the way open. Pneumatic and electric actions don't even theoretically
allow partial opening. I am not aware of any organ composition which calls for
partial opening.

IMO a filtered chiptune wave, with good quality reverb, makes a excellent
organ-like tone.

~~~
TheOtherHobbes
Organ partials aren't perfectly periodic. There's some chaotic pressure
variation around the lip, and the pipe also distorts mechanically with
pressure variations along the various possible modes - much more than a
stiffer instrument played with lower pressure, like a flute. So not only are
the partials subtly inharmonic in various ways, they also have different
attack envelopes at the start of a note, and the air pressure from the
bellows/pump may also vary over time as notes/ranks are played.

This is one of those common situations in music where a trivial model is too
superficial to capture the defining subtleties of a system. The richness of a
full pipe organ is a combination of subtle effects within each pipe, combined
with subtle variations within each rank, combined with the not-so-subtle
effect of combining multiple ranks, combined with the acoustic environment of
the hall, which doesn't just add a generic stereo reverb, but also supports
standing waves at some of the lower bass notes.

A filtered chiptune wave really isn't a very good approximation.

------
lispm
Nice.

Reader may be interested to hear how church organs from Bach's time sound. My
home town has two instruments, which can play this old music, such that it may
sound like back then:

Organ from 1736:
[https://www.youtube.com/watch?v=KkJRJ63_muk](https://www.youtube.com/watch?v=KkJRJ63_muk)

Organ from 1675:
[https://www.youtube.com/watch?v=izZ2DdshFZk](https://www.youtube.com/watch?v=izZ2DdshFZk)

~~~
gmueckl
I wonder how much continued maintenance has altered these instruments over the
centuries.

~~~
lispm
There was quite a bit of change over the centuries. But they were among the
first organs brought back to the baroque ideals and the original state as much
as possible. There is a lot of information about these efforts, but mostly in
German. Basically the Cosmae organ is now like it was in 1688. This was
finished in 1975 and influenced a lot of other instruments to be brought back
as close as possible to their original state.

[https://www.organartmedia.com/de/hus-arp-
schnitger](https://www.organartmedia.com/de/hus-arp-schnitger)

[http://www.orgelbits.de/huss-schnitger.html](http://www.orgelbits.de/huss-
schnitger.html)

------
makach
I would love to experience him hook up a c64 to an amplifier in a church and
play these songs. Would it sound the same as the recording on the website?

------
ce4
This should get tagged [2008]

~~~
kazinator
Also possibly [1685-1750]. :)

------
CGamesPlay
I'd love a "making of" follow-up. I would definitely be interested in a
comparison of a straight-up composition without the movement, energy, or
emphasis, and then adding to it in pieces to see the work come together.

------
jdkee
The original SID chips were amazing, as were the SSM and Curtis chips used in
the Prophet 5 Rev. 2 and 3.

