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 Forum index » DIY Hardware and Software » Developers' Corner
Another vocoder
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gasboss775



Joined: Jan 02, 2016
Posts: 217
Location: Scotland

PostPosted: Thu Oct 18, 2018 10:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Grumble wrote:
Have been working on this, but encountered a drawback:
There is a lot of noise induced by the processor and amplified by the input signal of the voice being to low (my educated guess).
I have to redesign and build proper input signal processing, get the impedance's and amplitudes right (5volt P/P)
Also I saw this in the datasheet:
REFH Input Resistance RREFH Digital Inputs = 55H, VREFH = VDD 1.2 kΩ
REFL Input Resistance3 RREFL Digital Inputs = 55H, VREFL = VDD 1.2 kΩ
but that seem to be covered by the input buffers.


I reckon an AGC circuit is probably a must to limit the dynamic range as the input is only capable of a fairly limited dynamic range ( assuming 8 bit your talking about only 48dB dynamic range ) but definitely make sure you're close to a maximum of 5 volts peak to peak.
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gasboss775



Joined: Jan 02, 2016
Posts: 217
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PostPosted: Thu Oct 18, 2018 11:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Here is an AGC using an lm13700 from the manufacturer's datasheet. It would probably require a low noise preamplifier if using with a microphone as the source.


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gasboss775



Joined: Jan 02, 2016
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PostPosted: Sun Nov 11, 2018 1:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

Grumble, have you made any more progress with this? I really think this is a great idea worth developing, hoping you haven't given up on it.
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Grumble



Joined: Nov 23, 2015
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PostPosted: Sun Nov 11, 2018 1:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

No I havent given up. This weekend I added an external 16bit ADC thinking it would give better results with lower amplitudes, but it didn’t.
So I guess the next thing is building an extra amplifier to increase the input signal amplitude.
But lately I have little time for working on this module because we have bought 2 puppie dogs. They claim most of my spare time....

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Grumble



Joined: Nov 23, 2015
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PostPosted: Sun Nov 11, 2018 10:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

After some thougts I decided to build the agc amplifier gasboss775 provided for me and make it into a small module with offsets and some leds to tell me what the amplitude of the output signal is.
And maybe remove the external adc because getting the data in the right order takes to much time, or maybe brush up my machine language programming...
Thank you!

edit:
There is no spare time at the moment to get soldering, but plenty of time to think about this project and I wonder what would be better, a AGC circuit or a compander like this one
Rolling Eyes

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Grumble



Joined: Nov 23, 2015
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PostPosted: Fri Nov 16, 2018 6:45 am    Post subject: Reply with quote  Mark this post and the followings unread

I added a compressor, and now it starts to sound like a vocoder..
The only thing is that due to the add of an external 16 bit ADC the sample time takes to long, well, not the sampling time but the conversion to usable data.
So maybe I'll go back to the internal ADC or I start working on my assembly....
In the demo I use a text to speech page reading a page from the Harry Potter books and a Solina module.
This is how it sounds:

https://youtu.be/RlpVbRhlYME

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blue hell
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PostPosted: Fri Nov 16, 2018 12:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Cool Getting there - nice!
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also .. could someone please turn down the thermostat a bit.
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gabbagabi



Joined: Nov 29, 2008
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PostPosted: Fri Nov 16, 2018 1:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

yeah, all good things takes some time,
also Roma wasn’t burnt down in a single day Cool
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gasboss775



Joined: Jan 02, 2016
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PostPosted: Wed Nov 21, 2018 5:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

Grumble wrote:
I added a compressor, and now it starts to sound like a vocoder..
The only thing is that due to the add of an external 16 bit ADC the sample time takes to long, well, not the sampling time but the conversion to usable data.
So maybe I'll go back to the internal ADC or I start working on my assembly....
In the demo I use a text to speech page reading a page from the Harry Potter books and a Solina module.
This is how it sounds:

https://youtu.be/RlpVbRhlYME


If you are compressing the audio prior to sampling I think the built in ADC should be adequate.

Good to see you're still pursuing this one, despite canine interruptions! Very Happy
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Grumble



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PostPosted: Thu Nov 22, 2018 5:18 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm thinking about what to do next... I have some other things in the pipeline as well...
Maybe let it rest for a while and ponder about this some more... Rolling Eyes

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Grumble



Joined: Nov 23, 2015
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PostPosted: Sat Feb 02, 2019 3:09 am    Post subject: Reply with quote  Mark this post and the followings unread

I just picked up the thread of the vocoder: I have 4 Max260 dual switched capacitor filters in my drawer, suitable for 8 2nd order filters. I will use them as bandpass filters, with programmable quality factor and clocked each filter with an ICM7555 that makes it easier to play with different bin types (linear or exp.)
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Grumble



Joined: Nov 23, 2015
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PostPosted: Mon Feb 18, 2019 5:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Posted Image, might have been reduced in size. Click Image to view fullscreen.

from top lef to top right: An Arduino Nano, below the nano a dc/dc converter for -5 volt that is needed for the filters (this was before I desided to go Euro format) next to the Nano an AD8804 trimdac, above the trimdac a quad opamp, now a LM324 but this will be exchanged for a better rail to rail quad opamp.
Next are 4 max260 dual programmable filters. They are set for a division of 200 of the clock frequency. The most left filter is used as a low pass ánd as a band pass filter, the most right on is used as a band pass filter ánd a high pass filter, the other 6 filters are just bandpass filters, so I end up having 10 second order filters.
The low row of chips are 8x ICM7555 in astable mode, they are used to set the center frequency of the filters, this way I am flexible to the use of bins, be it lin or oct.

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Last edited by Grumble on Mon Feb 18, 2019 7:54 am; edited 1 time in total
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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Mon Feb 18, 2019 7:37 am    Post subject: Reply with quote  Mark this post and the followings unread

you should have put a NSFW tag on that post Razz

(btw I can't access the MAX260 fadatasheet on your C: drive)

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Grumble



Joined: Nov 23, 2015
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PostPosted: Mon Feb 18, 2019 7:55 am    Post subject: Reply with quote  Mark this post and the followings unread

oops, thanks Embarassed
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blue hell
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PostPosted: Mon Feb 18, 2019 12:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh dear .. and I looked at it while at work Laughing

That is a bloody compact vocoder thingie!

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also .. could someone please turn down the thermostat a bit.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
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Grumble



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PostPosted: Mon Feb 18, 2019 12:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

There will be another board on the backside of this one with potmeters, connectors and mixers...
And.... I’m still not sure if it will work Rolling Eyes

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blue hell
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PostPosted: Mon Feb 18, 2019 12:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

As Jan Boerman (dutch composer) once said .. het doel van het experiment is het vaststellen van de aard van de mislukking

(the purpose of the experiment is to determine the nature of its failure)

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also .. could someone please turn down the thermostat a bit.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
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Grumble



Joined: Nov 23, 2015
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PostPosted: Fri Feb 22, 2019 8:10 am    Post subject: Reply with quote  Mark this post and the followings unread

To keep learning from mistakes: I just removed the DC/DC converter because it introduced a huge amount of noise which I couldn't get rid off.
Placed a ua7905 instead. Was easy because I use the eurorack power supply connections (+12 volt, gnd and -12 volt)

Posted Image, might have been reduced in size. Click Image to view fullscreen.
Also started working on the front board placing potmeters and connectors.

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gasboss775



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PostPosted: Wed Jul 10, 2019 12:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nice work Grumble, glad to see you're still pursuing this idea.
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gasboss775



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PostPosted: Wed Jul 10, 2019 12:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

gasboss775 wrote:
Nice work Grumble, glad to see you're still pursuing this idea.


Also, but a bit off topic. After many uneasy years of using veroboard ( stripboard ) I have found these matrix boards to be far easier to work with, no more track shorts!
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