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



Joined: Jan 02, 2016
Posts: 212
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: 212
Location: Scotland

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
Posts: 212
Location: Scotland

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
Posts: 833
Location: Netherlands
Audio files: 27

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
Posts: 833
Location: Netherlands
Audio files: 27

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
Posts: 833
Location: Netherlands
Audio files: 27

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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Joined: Apr 03, 2004
Posts: 22598
Location: The Netherlands, Enschede
Audio files: 224
G2 patch files: 319

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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g.gabba



Joined: Nov 29, 2008
Posts: 464
Location: berlin
Audio files: 23

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
Posts: 212
Location: Scotland

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



Joined: Nov 23, 2015
Posts: 833
Location: Netherlands
Audio files: 27

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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