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Renoise midi clock to control voltage?

midi to cv analogue syncing Linux

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#26 TheBellows

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Posted 08 September 2017 - 17:16

Thanks Bellows!

 

I downloaded the official Datasheet for the chip and was reading it yesterday.  Have to say, I don't like the idea of it having a built-in amplifier with no way to bypass it.  Wouldn't the levels need to be taken down before connecting it to something like, say, a multitrack recorder input?

 

Having an amplified output would mean it's way above line-level, wouldn't it?

Still learning this stuff but I can imagine the distortion would be insane!

It's a lot better to have an amplified output than a too low output. The signal out will be about 5 volts at max output, while a line output is around 1 volts and if you feed a signal that peaks at 5 volts into a line in, then you would most likely end up with a lot of distortion/clipping. However this is very easy to fix with some resistors/potentiometers.

 

In some cases an amplified output that is too loud is very beneficial, like for instance if you want it to go through a passive EQ circuit. A passive EQ circuit is pretty easy to create, but it requires a louder signal than an active EQ circuit (which basically is a preamp or several preamps and a passive EQ circuit). An EQ circuit is basically just some potentiometers and some capacitors. 

If you are going to use the signal to feed several line inputs it will also be beneficial, in basic you only need to add a potentiometer to each input.

Think of the potentiometer as a mixing device, it's got line in, which is the middle taper that moves across the graphite (the middle pin of the potentiometer). It's got a line out, which goes to the line in of whatever you are feeding the signal into. It can be on either side, it's up to you, but the usual way would be to turn up the volume clockwise. The last pin goes to ground. If you look at the potentiometer from the top, pins facing upwards, it would be pin left to ground, middle pin is line in and the right one is the line out. You could also swap the line in and line out, it doesn't really matter. Find the way you like and stick with it, it's easy to solder the wrong way and you realize just when everything is screwed together. 

You might need an extra resistor to prevent it from going too loud, but that depends on what you have in the other end. It could be wise to use a trimpot, maybe 50K and preferably multiturn pots so you can finetune it easily at any time from 0 to 50K which should be enough. this one shold not be connected to ground, as that is the first potentiometers job. If you use a small value on the potentiometer it will act as a filter and remove higher frequencies, so it might be wise to use higher value potentiometers such as 500K. Preferably it should be a A500K which has a logarithmic curve. If signal has zero resistance to ground, then it's completely lost and should in theory be completely silent. 



#27 Renoised

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Posted 08 September 2017 - 18:35

Thanks, I even understood that!

 

I'll have to get the electronics stuff out again, cause I shoved it aside while I was doing other stuff.  Last thing I was trying to get my head around was impedance, so I'll carry on from there I think.  And I was looking into the most basic way to convert DC into AC cause I read that a lot of the DIY synths out there are outputting a DC voltage, but ideally, the voltage should be converted to AC to drive a speaker.


Edited by Renoised, 09 September 2017 - 10:28.


#28 TheBellows

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Posted 09 September 2017 - 00:54

Thanks, I even understood that!

 

I'll have to get the electronics stuff out again, cause I shoved it aside while I was doing other stuff.  Last thing I was trying to get my head around was impedence, so I'll carry on from there I think.  And I was looking into the most basic way to convert DC into AC cause I read that a lot of the DIY synths out there are outputting a DC voltage, but ideally, the voltage should be converted to AC to drive a speaker.

Impedance is quite complicated and isn't something you need to worry about too much as long as you use circuits that work properly and is designed by someone who knows their shit. Just about any proper audio circuit has a high input impedance and a low output impedance and as long as you use the proper power supplies and proper grounding, and everything then it should be fine. 

 

I think the problem you're referring to is that audio signals from crappy circuits can have DC offset and clipping problems. 

You should never play DC through your speakers. DC is inaudible except from the initial click and the sound of your speaker frying. Audio is AC and should not have any DC at all, but if a DC is introduced to your audio signal creating a DC offset then you probably have some bad circuitry causing it. 



#29 Renoised

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Posted 09 September 2017 - 10:36

No I meant that I was intending to play around with basic oscillators and driving a speaker etc.  I started there mainly because I wanted to be able to hear the results of experimentation.  I can't remember which one it was, but there was one where someone showed a basic oscillator circuit but pointed out it's not ideal for driving a speaker due to it being DC, and crazy as it might sound I'm pretty sure he said it lacks a current.  He mentioned something about using an opamp to create a buffer that would either convert the output to AC or give it a current.  I'm pretty sure it was one of those two reasons but can't remember which.  It might even have been for both reasons.

 

So that's what I was looking into at the time; trying to get my head around what an opamp buffer does and to understand impedance.

 

EDIT:

 

Ah yes!!!  It was that Casper Electronics guy on YouTube, or at least I think it was, so what I'm talking about is probably in one of these videos.  I think I might buy the kit from him actually, to have a play around with this.  He's very good at explaining stuff and generous at what he taught.  In these three videos alone, he teaches how to create oscillators, sequencers, and samplers - very cool stuff!

 


Edited by Renoised, 09 September 2017 - 13:36.


#30 Renoised

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Posted 09 September 2017 - 15:22

Yup, it was indeed Casper Electronics, although I was mixed-up regards what he meant.

 

If you look at the "Important Note" on this page you'll see the stuff about the buffer:

http://www.bastl-ins.../omsynthvideo1/

 

BTW, Bellows, you should definitely check-out this entire project if you haven't already cause each one of those videos has a related page on their website and it might even give you some ideas how to go about getting what you asked about in your original question.



#31 TheBellows

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Posted 09 September 2017 - 15:28

No I meant that I was intending to play around with basic oscillators and driving a speaker etc.  I started there mainly because I wanted to be able to hear the results of experimentation.  I can't remember which one it was, but there was one where someone showed a basic oscillator circuit but pointed out it's not ideal for driving a speaker due to it being DC, and crazy as it might sound I'm pretty sure he said it lacks a current.  He mentioned something about using an opamp to create a buffer that would either convert the output to AC or give it a current.  I'm pretty sure it was one of those two reasons but can't remember which.  It might even have been for both reasons.

 

So that's what I was looking into at the time; trying to get my head around what an opamp buffer does and to understand impedance.

When you oscillate a DC signal it's not DC anymore, so how can an oscillator circuit 'be' DC? Almost all small circuits are driven by DC, but an audio signal is always AC, it can't be both at the same time. If the audio signal has DC offset however, the voltages rises while volume/dynamics of the audio decreases, which is not good. Bad circuitry can of course cause things like this, so to avoid it you should stick with circuits you know works. Ready made modules makes this easy, while building your own from random circuits you find on the net however can often lead to problems.

An op amp is a common integrated amplifier that increases the amplitude, it's basically a preamp on its own. It however is driven by both positve and negative voltage sources, which makes the circuits a bit more intricate and makes it harder to figure out how to make them interact properly with different circuits. Ready made modules should have all this sorted out with only one power supply, so that makes things easier.

I wouldn't use opamps for oscillating, i'd rather start with 555 oscillators, much more fun to play around with. Then i'd buy something like a function generator IC, i strongly recommend XR-2206, it's one chip that can produce all sine, triangle and square wave and it's super easy to work with, just build one of the circuits in the datasheet. 

One cool suggestion would be to make an LFO out of a 555 timer chip that controls an LED, then turn it into a photocoupler and let the output of the photoresistor control the volume of the XR-2206. To make it even cooler you could connect an IR-phototransistor to the control voltage pin of the XR-2206 and hook up an IR LED to a power source, now you can control the pitch with your hand like a theremin only with IR light.


Edited by TheBellows, 09 September 2017 - 16:04.


#32 Renoised

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Posted 09 September 2017 - 15:46

When you oscillate a DC signal it's not DC anymore, so how can an oscillator circuit 'be' DC? Almost all small circuits are driven by DC, but an audio signal is always AC, it can't be both at the same time.

 

I wish people would say stuff like that when they teach this stuff :D

 

Cheers mate, never thought of it like that, and what you jsut said made other stuff mentally fall into place!

BTW, I think you missed the other post I just slipped in again :P

 

Yup, I totally got it wrong - duh :lol:



#33 TheBellows

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Posted 09 September 2017 - 18:11

It might be a bit inaccurate to put it that way, because even though it's an AC signal it can still be very close to a DC signal. A square wave oscillator is in fact DC only in pulses. If played in high enough frequencies it becaomes audible, but below the audible frequencies it acts like a continuous on and off DC switch. DC is when the audio is like a flat road while audio is like the ocean. Audio should always be centered at zero or else it has DC offset which can cause clicks, distortion, weaker volume and all that crap. The further away from being sentered to zero the worse it will sound. You can fix it with a highpass filter, but it may already have destroyed the audio. 

If you want to make an oscillator for actual music/audio production, then i suggest sticking with a function generator module or the chip i mentioned, as you won't have to deal with the problems from bad ciruitry.

 

I think i will order a cheap oscilloscope thingy soon, it could be very useful to see how the waveform looks like. I saw some ridiculously cheap ones at aliexpress, but i'm not shure...


Edited by TheBellows, 09 September 2017 - 18:26.


#34 Renoised

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Posted 11 September 2017 - 01:54

Can you just clarify my thinking here for me, Bellows?

 

Looking at a signal on an oscilloscope, I have it in my head that a waveform that falls either completely above or completely below the center line is DC, and anything that has the line running through the center is AC.  Assuming that is correct then what you're saying is that when something deviates further and fruther from the centre is gaining a larger and larger DC offset, right?

 

BTW, that chip looks cool, I started looking into it but I found another which appears to be even better cause it has Saw and pulse width modulation whereas the othe doesn't.  It's called ICL8038 if you fancy taking a look, I think it's the same sort of thing, looks like it from the spec sheet.  Regards the oscilloscope, I actually have the same model he uses in the videos although I've not built mine yet, and I purchased it as a kit!  Have to say though, I'm pretty sure it's a decent piece of kit as lots of people use them and I've never seen a bad review about one.  It's not as good as having an analogue oscilloscope would be, obviously, but for the money it appears to be quite neat!



#35 TheBellows

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Posted 11 September 2017 - 10:07

Can you just clarify my thinking here for me, Bellows?

 

Looking at a signal on an oscilloscope, I have it in my head that a waveform that falls either completely above or completely below the center line is DC, and anything that has the line running through the center is AC.  Assuming that is correct then what you're saying is that when something deviates further and fruther from the centre is gaining a larger and larger DC offset, right?

 

BTW, that chip looks cool, I started looking into it but I found another which appears to be even better cause it has Saw and pulse width modulation whereas the othe doesn't.  It's called ICL8038 if you fancy taking a look, I think it's the same sort of thing, looks like it from the spec sheet.  Regards the oscilloscope, I actually have the same model he uses in the videos although I've not built mine yet, and I purchased it as a kit!  Have to say though, I'm pretty sure it's a decent piece of kit as lots of people use them and I've never seen a bad review about one.  It's not as good as having an analogue oscilloscope would be, obviously, but for the money it appears to be quite neat!

Sound just about right. The simplest way to put it i think is to say that if the sum of the negative and the positive phase is zero then you have a DC balanced signal.

 

I haven't seen the chip you mentioned, it's datasheet says it's obsolete, but it looks like it's still being sold. I ordered a couple myself to check them out.

Another chip that looks interesting is the SN76477 (or ICS76477) , an old chip used as a sound generator in arcade games and such. It seems to work like a complete synthesizer in one chip, with envelope generator, LFO, noise generator and oscillator. 


Edited by TheBellows, 11 September 2017 - 11:33.


#36 Renoised

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Posted 11 September 2017 - 17:35

Didn't realise it was obsolete, lol, never saw that (I ordered four of the things) :rolleyes:

Will check-out the others you mention although it would be much cooler to know about current production chips that are designed to be complete synthesizers if you know of any!

 

Thanks for the heads-up on the AC/DC thing :)



#37 TheBellows

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Posted 12 September 2017 - 16:55

Didn't realise it was obsolete, lol, never saw that (I ordered four of the things) :rolleyes:

Will check-out the others you mention although it would be much cooler to know about current production chips that are designed to be complete synthesizers if you know of any!

 

Thanks for the heads-up on the AC/DC thing :)

They don't make much of these kind of things anymore, digital has taken over. SN76477 isn't that expensive atm, so you better get some before they become rare. 


Edited by TheBellows, 12 September 2017 - 16:58.


#38 Renoised

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Posted 14 September 2017 - 20:28

Digital will never take over, it's just popular due to it's cheapness etc, and actually, they just started manufacturing the original design analogue chips used in the famous analogue synthesizers of the 70s and 80s again, all brand new, all available to use in your own designs etc!

 

Looks like the good times are on the way back :walkman:



#39 TheBellows

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Posted 15 September 2017 - 15:19

Analogue is still used in guitar pedals and such and it's always going to be a part of the circuitry in musical equipment, but in the whole picture it's just a small niche.

It's not that expensive to reprint an IC if you already have the masks for it, but don't expect new analogue ICs to be developed and germanium transistors are almost obsolete and very expensive.

Lots of older parts are much less accurate than the newer parts that has taken their place. Accuracy is not the reason why we want to use analogue equpiment for audio and if you're redesigning an old circuit with modern replacement parts it won't sound the same. For instance i believe you can make a better simulation of a germanium based fuzz pedal digitally than if you're building it with silicon transistors.

I'm no expert on the subject, so i might be wrong and i'm not on the level of making really high end musical equipment as it's just a hobby and i want to make it cheap and simple. 

I'm still hoping for a new stock of the 6581/8580 SID chip (C64), there is a replacement chip made for it that digitally emulates the SID, but it's not really what i'm looking for.

The chip SN76477 is the closest i can come to the SID that is cheap and easy to find stll.

 

When i talked about new vs old components it's mainly the transistors, diodes and integrated circuits that has changed. Some sellers, selling old parts, advertise with 'better sounding resistors' or whatever, but that's just bs. Maybe you can hear some difference between different types of capacitors in some circuits, but you could hardly say that one sounds better than the other.


Edited by TheBellows, 15 September 2017 - 15:36.






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