electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Articles  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links  |  Store
Forum with support of Syndicator RSS
 FAQFAQ   CalendarCalendar   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   LinksLinks
 RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in  Chat RoomChat Room 
 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Audio Signal and CMOS Ground
Post new topic   Reply to topic Moderators: mosc
Page 1 of 1 [6 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
jean-louise



Joined: Apr 27, 2009
Posts: 73
Location: berlin
Audio files: 2

PostPosted: Sat Oct 26, 2013 1:56 am    Post subject: Audio Signal and CMOS Ground Reply with quote  Mark this post and the followings unread

Hello!
I am a bit confused about the relation of the respective ground and negative rail in CMOS and audio circuits.
AFAIK a typical audio signal swings from V+ to V- around 0V. This is achieved with circuits using a bipolar power supply, where 0V in the middle is ground.
The Lunetta/CMOS-circuits all have a unipolar supply, also with 0V as ground but also as the negative extreme.
From what I gathered in the Lunetta world there is no real distinction between a digital (data) signal - the 0s and 1s - and a square wave audio signal. Also it seems like because it's all squarewaves at maximum volume there is not much of a need for a reference in the middle.
But what happens when I interface a Lunetta to an audio circuit like, e.g., an amp? Would then the negative half of the squarewave sit at ground and only the positive swing would be left?



Any help to deconfuse me would be very appreciated.
Back to top
View user's profile Send private message
Blue Hell
Site Admin


Joined: Apr 03, 2004
Posts: 20274
Location: The Netherlands, Enschede
Audio files: 143
G2 patch files: 318

PostPosted: Sat Oct 26, 2013 5:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes ... it's all above ground typically for CMOS stuff, but when you couple the signals out through a capacitor it would level out around zero. Most amps or computer audio interfaces would have an input capacitor anyway, so that'd be arranged automagically Smile


To make sure you could add your own output cap of course .. hmm .. you want to know a value now I guess ... I'd start with around 10 µF ... the polarity direction .. + on CMOS side seems best ... when not enough bass increase it, but can't imagine that to be necessary.

_________________
Jan
Back to top
View user's profile Send private message Visit poster's website
jean-louise



Joined: Apr 27, 2009
Posts: 73
Location: berlin
Audio files: 2

PostPosted: Sat Oct 26, 2013 7:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thank you!
Yeah, in the meantime I had begun to suspect something like a coupling capacitor would be beneficial.
But this reminds me again of how little I understand of the whole thing.
So for example if I have an squarewave osc going between 5V and 0V after coupling the circuits the 5V is interpreted as 2,5V and the 0V is interpreted as -2.5V?
How fast must the oscillation be to be interpreted as AC, does that depend on the capacity of the coupling capacitor?
In other words:
Is there a good read up about capacitors and capacitor coupling online anywhere, but, like, for dummies?
Back to top
View user's profile Send private message
Blue Hell
Site Admin


Joined: Apr 03, 2004
Posts: 20274
Location: The Netherlands, Enschede
Audio files: 143
G2 patch files: 318

PostPosted: Sat Oct 26, 2013 7:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Good questions Smile

its bed time now tho .. but questions like yours eventually led to filter theory and all ... ok, for now ,,, the basics are .. it is an RC filter, the R being input or output impedance of your circuit, the C being the capacitor you throw in .. it really is just a handful of 'laws' and a bit of math ... Ohm, Faraday, Norton, Thevenin, Kirchhof .. that's about it ...

but yes .. a 50% duty cycle square would do as you described, a slow square would on average do the same, but it would distort the wave form too .. for your perception that would just kill some bass tho ... ah there is another 'law' I forgot ... Fourier .. about how arbitrary waves can be composed from sines .. harmonic sines even.

Anyway, that'd give some hints to google a bit and I'm off to bed for real now - if questions I'd try to explain it a bit of course, later Smile

_________________
Jan
Back to top
View user's profile Send private message Visit poster's website
jean-louise



Joined: Apr 27, 2009
Posts: 73
Location: berlin
Audio files: 2

PostPosted: Sat Oct 26, 2013 7:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks again! OK, I'm off to google

and good night
Back to top
View user's profile Send private message
varice



Joined: Dec 29, 2004
Posts: 711
Location: Northeastern shore of Toledo Bend
Audio files: 22
G2 patch files: 49

PostPosted: Sun Oct 27, 2013 1:20 am    Post subject: Reply with quote  Mark this post and the followings unread

jean-louise wrote:
...So for example if I have an squarewave osc going between 5V and 0V after coupling the circuits the 5V is interpreted as 2,5V and the 0V is interpreted as -2.5V?...


Yes, especially if the fundamental frequency of the square wave is well above the corner frequency of the RC filter formed by adding an AC coupling cap.

As Jan says, adding a capacitor in series with the signal (and taking into account the input impedance of your audio amp) will actually form an RC filter, in this case, a single pole high pass filter. Audio (AC) frequencies above the corner frequency of this filter will be passed through, while frequencies below will be attenuated at 6dB per octave, and any DC signal offset (which is inaudible, but can cause problems) will effectively be blocked. The capacitor employed in this fashion is usually referred to as AC coupling cap, but IMHO, I prefer to call it a DC blocking cap, as that is really its primary purpose.

Also as Jan mentions, many audio amps already have an AC coupling (DC blocking) cap at the input, so it is probably unnecessary to add one to your Lunetta logic synth output. But if you want to add this cap to your Lunetta output anyway, you can calculate the high pass filter characteristics by using the following online calculators:

http://www.muzique.com/schem/filter.htm

http://www.vk2zay.net/calculators/rc.php

_________________
varice
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: mosc
Page 1 of 1 [6 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
emSynth

Please support our site. If you click through and buy from
our affiliate partners, we earn a small commission.


Forum with support of Syndicator RSS
Powered by phpBB © 2001, 2005 phpBB Group
Copyright © 2003 through 2009 by electro-music.com - Conditions Of Use