Posted: Tue Feb 10, 2015 2:12 pm Post subject:
16-Tone-Divider Subject description: generate a 16-tone Lunetta scale with only two chips
I am really into dividers right now and experimented a bit more with the idea from the Gong-Drone circuit. First I came up with a simple circuit that divides by 4,5,6 or 7. Simple means that it has minimum parts, in particular, works with only half of a 4520 and half of a 4066 without using additional logic gates. I played around with this divider for a while and then wondered if it wouldn't be possible to extend that idea to 16 tones. There was still the other half of the 4520 to use for that.
Initially I tried cascading two dividers, but the resulting scale always ended up with duplicate tones. Finally, I came up with the idea shown in the circuit below. It needs only two chips and a few parts. The first divider is simply a divider by 8,9,10,11,12,13,14 and 15. The result is then sent to a divider by 2 or 4. This way there was no overlap of the tones in the scale any more. It is actually necessary to use a second divider following, because the divided input is available only with the reset signal, and that signal is very short and doesn't sound good yet.
Here is how the first divider works: the clock signal is sent to a 4520 counter U1A. The counter has a reset logic that would reset it via Q3 and R1 when it reaches 8. However, if any of the 4066 analog switches is open, a 0 at the corresponding counter output will prevent the signal to reach the necessary level to trigger a reset. Only when none of the outputs combined from the analog switches is a 0, the reset signal will be high enough to reset the counter. Because there might be multiple switches open, I added diodes to the outputs before combining them. This works similar to a Diode-Resistor-Logic AND gate, or a pass gate. This works without glitches because the 4520 is a synchronous counter and the outputs will change together. Depending on the control signals for D0 to D2, the counter resets at 8,9,10,11,12,13,14 or 15 and the divided input frequency is available with the reset signal.
The second divider then turns the output from the first divider into a nice square wave again and divides it by 2 or 4. This also doubles the range to 16 tones. I had to use a dirty trick to achieve that. The Q0 output of the second counter U1B is sent to the circuit OUT via a 10K resistor R2. When the second divider changes to a division by 4, the Q2 output is added to it via an analog switch. It acts like a pass gate and this way I didn't need a selector to do the job. You can see the remains of Q0 on the scope, but you don't hear them. Also, the output signal can be used to drive other CMOS gates without a problem.
The division is selected by inputs D0 to D3 which can be fed by a counter or other gates (e.g. by 4 oscillators for a 16 tone melody generator). Because of the way the circuit works, the lowest divider is selected by D=0000, which results in the highest tone. I used the inverted outputs from a 4040 to drive the D0..D3 inputs, so the scale is played starting at the lowest tone. The recording demonstrates the scale with an input frequency of about 13 KHz.
The schematic includes the calculation for the output frequencies that would result from an input frequency of exact 13200 Hz. You can use other inputs frequencies of course, the ratio between the tones will be the same. Mind that the tones are not notes. They do not match the note frequencies exactly, sometimes are even right in between two notes. Nevertheless, this is just what I was looking for to use in my next Lunetta build and the fixed ratios will even provide harmonic pairs in this scale.
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Ah, micro tonal stuff, a couple of those would generate nice harmonies indeed :-) _________________ Jan
also .. could someone please turn down the thermostat a bit.
Joined: Apr 23, 2015 Posts: 184 Location: Perth, Australia
Posted: Sat Aug 29, 2015 6:46 pm Post subject:
I don't know if this is of interest but here is a table of master clock frequencies and the Just Intonation notes that can be produced. The note frequencies I have used are open to debate. In each case I have tried to select the frequency that gives the maximum number of useful ratios but some notes, F# in particular, just have no really outstanding choices. Of course unlike Even Temperament some chords are less tuneful than others. See https://en.wikipedia.org/wiki/Just_intonation.
With a choice of 4 master clocks you can get a full 2 octaves of Just tuned notes.
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Useful master clocks for synaesthesia's 16 note divider.
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Same idea, but much simpler implementation this time. Just tested this on a breadboard and it does work. This is a programmable divider by 4, 5, 6, or 7.
When used with an extra XOR as frequency doubler at the input of the counter, you can even get divisions by 2, 2.5, 3, and 3.5.
The division is controlled by the two logic levels at inputs CTRL. A logic HIGH prevents the relevant counter output from delaying the RESET signal.
So with a frequency of 880Hz (A5) at the input, you will get roughly 440Hz (A4), 352Hz (F4), 293Hz (D4), and 251Hz (a bit above B3) at the output.
The optional mixing of Q0 and Q1 makes the output sound less harsh. For input to a counter you would use Q2 only, but mind that the duty cycle is not 50%.
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Joined: Feb 02, 2010 Posts: 266 Location: California
Posted: Mon Jun 27, 2016 10:21 pm Post subject:
This is cool. I have looked at the counter chips to see if I could accomplish something like this, but couldn't come up with a simple way to do it.
I did an 8 note one with a 4051 (one of eight switch) setting the reset point on a 4017 (I think I used counts 3,4,5,6,7,8,9,10 for my notes) with a high frequency clock feeding it.
I then ran the output of that into a variable wave generator that I made with another 4017 with pots on the outputs like a step sequencer, to shape amplitude levels on each output, in order to make uniform wave shapes out of the pulsewidth shifting output of the variably reset 4017.
It obviously needs a pretty high frequency "top octave" clock to do all that dividing.
The results of that are in the solar synth in progress that I posted about here. _________________ ∆ A.M.P. ESOTERIC ELECTRONICS ∆
This divider has nice properties. It does need a rather high input clock frequency, but the divisions by 8, 9, 10, and 12 create nice harmonics, and the output from Q2 has a duty cycle between 33% and 50%.
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