[sdiy] AD/DA schematics? quantizers,etc

Thu May 14 20:12:58 CEST 2009

ok

i changed some things and got something i am very very happy with

it might not be 100 percent accurate but it is getting good melodies out of a slow moving lfo

i ditched the output offset first of all

second i changed the DAC to 10 v ref

third i took out the cap going out

fourth i messed with the duty and timing of the clock

there is much work to be done but i highly appreciate everyones help!!!

you have made me understand!

--------------------------------------------
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http://www.myspace.com/lossnyc

(updated monthly)

http://www.soundclick.com/lossnyc.htm

http://www.indie911.com/dan-snazelle

(or for techno) http://www.myspace.com/snazelle

ALSO check out Dan synth/Fx projects:

AUDIO ARK:

www.youtube.com/watch?v=TJRpvaOcUic

www.youtube.com/watch?v=BqIa_lXQNTA&feature=channel_page

www.youtube.com/watch?v=V4nJPjGgOcU&feature=channel_page

and soundtrack/design work:

NEW: check out Dan's sound design from the 1998 award winning film SAFARI by catherine chalmers

http://www.catherinechalmers.com/videos.cfm

----------------------------------------
> From: jerryge at cableone.net
> To: synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] AD/DA schematics? quantizers,etc
> Date: Thu, 14 May 2009 11:47:11 -0500
>
> I am sure the staircase is excellent but what I am referring to is matching
> the output steps to note voltages.
>
> This stuff is only important if you are a perfectionist.
>
> Take a theoretical VCO in perfect tune at 1volt per octave using -5v to +5v
> as its input range. Each octave has 12 semitones or notes, this means that
> each increase of .08333... volts will increase the frequency by exactly one
> semitone (1volt/12semitones). If each step (100 cents) (or 2 steps 50 cents)
> is at this voltage you are half way there. The drawback is that the
> transitions are right on the note and bit jitter can cause you to be 50 to
> 100cents (a full semitone) off the note. If you center the desired voltage
> ( a multiple of .08333... volts ) in the "flat" part of the step instead of
> the transition bit jitter in a "quite" system is no problem. An easy way to
> do this is to add 1/2 of the .08333... volts on the input. You can match 2
> "steps" to .08333... volts by setting up the converter(s) to divide evenly
> by the number of semitones in the full 10 octave range. 10 Octaves with 12
> Semitones each = 120. An 8 bit converter has 255 "steps" so you can use
> 2*120 or 240 steps and hit the semitones square on. To do this all you need
> to do is set the converter(s) so that -5v = 0 steps and +5 = 240 steps. Of
> course this requires that you use precision reference voltage(s) and limit
> circuit noise as a variation of 8.333...e-4 volts on the output is One Cent
> and people with "perfect pitch" can hear a variation of 3 Cents (0.0025
> volts). The other consideration is using multiple voices with minor pitch
> variation causes sub harmonics that even us mortals with far less that
> "perfect pitch" can hear.
>
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Matthias
> Herrmann
> Sent: Thursday, May 14, 2009 10:50 AM
> To: Synth-Diy
> Subject: AW: [sdiy] AD/DA schematics? quantizers,etc
>
>
>> Make perfect sense to me and sounds like a solid design.
>> As long as you are not using the control voltage to run a VCO at
>> 1v/o you do
>> not have to be concerned about where the output voltages make transitions.
>
> i do! and the staircase tracks nice over 10 octaves (at least for me it is
> okay, i did not do exact measurements, though).
>
> cheers,
> matthias
> ___
> www.modular.fonik.de
>
>
>>
>> It had slipped my mind that some control voltages are -5 to +5 and others
>> are 0 to +10v.
>>
>>
>> -----Original Message-----
>> From: synth-diy-bounces at dropmix.xs4all.nl
>> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of
>> Matthias.Herrmann at jeppesen.com
>> Sent: Thursday, May 14, 2009 10:02 AM
>> To: synth-diy at dropmix.xs4all.nl
>> Subject: RE: [sdiy] AD/DA schematics? quantizers,etc
>>
>>
>> i did not follow the whole thread, however i am currently working on a
>> quantizer that would be usable for control votages in the range of -5V to
>> +5V.
>>
>> i used a DAC0800, that is setup to operate in a bipolar mode (output from
>> -5V to +5V using a REF102 10V reference). as we already learned the output
>> is not exactly 10V p-p when using only 7 bits, therefor i added an
>> invering mixer with offset and gain control to trim the DACs output to
>> exactly -5V to +5V.
>>
>> hope that makes any sense in this context. as said above i did not follow
>> the thread toroughly. sorry.
>>
>> cheers,
>> matthias
>> ___
>> www.modular.fonik.de
>>
>>
>>
>>
>> synth-diy-bounces at dropmix.xs4all.nl wrote on 05/14/2009 04:46:36 PM:
>>> <
>> vref
>>> in
>>> this schematic.
>>> This does not take care of any Offset you may have.>>
>>> ====
>>> That's not quite right - with a 10v vref you still need to scale the
>> output
>>> but the factor is
>>> (OUT 10v/9.412v = 1.06)
>>> ====
>>>
>>> -----Original Message-----
>>> From: synth-diy-bounces at dropmix.xs4all.nl
>>> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Jerry
>>> Gray-Eskue
>>> Sent: Thursday, May 14, 2009 9:33 AM
>>> To: Synth-diy at dropmix.xs4all.nl
>>> Subject: RE: [sdiy] AD/DA schematics? quantizers,etc
>>>
>>>
>>>
>>> I should not try to do math at midnight when I am tired. I have a couple
>> of
>>> inaccuracies in the message below.
>>>
>>> 1 The "Step" value of an 8 bit converter with 5v ref should be 5v/255
>> not
>>> 5v/256 ~= 0.0196078 volts. This in turn modifies the Scale Factors (IN
>>> 4.706v/10v = .4706) (OUT 10v/4.706v = 2.125) Note:"Step" 240 = 0.01960v
>> *
>>> 240 steps = 4.705872 ~= 4.706
>>>
>>> 2 Do not "SUBTRACT 0.01v" on the back end, this would null out Centering
>> the
>>> desired values on the steps and throw all the output "Steps" off 1/2
>> "Step"
>>> and off "Note"
>>> ========
>>> IF you setup your DAC0808 as in the Data Sheet- FIGURE 1. +10V Output
>>> Digital to Analog Converter You will see that the DAC0808 Can take 10v
>> for
>>> Vref+ SO things get simpler You only need to do the FRONT END scaling
>> into
>>> the A to D
>>>
>>> The Scaling is already in place on the BACK END D to A using the 10v
>> vref in
>>> this schematic.
>>> This does not take care of any Offset you may have.
>>> ========
>>> To clear up Offset and Scaling -
>>>
>>> Offset is a DC voltage in an audio signal that pushes the waveform away
>> from
>>> centering on 0 volts, Typical audio signals run balanced amounts of +
>> and -
>>> voltages. Mathematically this is ADDITION or SUBTRACTION of a Fixed
>> Value to
>>> ZERO out the offset, Decoupling Caps may also be used to remove offset.
>>>
>>> Scaling is MULTIPLYING or DIVIDING a value to change its overall peak,
>> or
>>> peak to peak voltage.
>>> =======
>>>
>>>
>>> -----Original Message-----
>>> From: synth-diy-bounces at dropmix.xs4all.nl
>>> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Jerry
>>> Gray-Eskue
>>> Sent: Thursday, May 14, 2009 12:03 AM
>>> To: Synth-diy at dropmix.xs4all.nl
>>> Subject: RE: [sdiy] AD/DA schematics? quantizers,etc
>>>
>>>
>>>
>>> Let me try to clear up the Vref thing for you.
>>>
>>> If you are just running audio signals through the converters all you
>> need to
>>> do is scale down the 0-10v to 0-5v run it into the A to D run the Data
>> lines
>>> into the D to A and scale the output back up to 0-10v, the drawback here
>> is
>>> that the audio signal is running with a 5v offset and needs to have that
>>> removed either by subtracting the voltage or using capacitive coupling
>> into
>>> your amplifier.
>>>
>>> If your analog signal IN is centered on 0v i.e. -5v to +5v your scaling
>> will
>>> need to scale the input down to -2.5v to +2.5v and Add a 2.5v offset so
>> that
>>> the signal into the A to D is 0v to 5v. In this setup vref+ = 5v and
>> Vref- =
>>> 0v is good. Again the offset needs to be removed.
>>>
>>> Now If you are tiring to quantize a Control Voltage and want it to "Hit
>>> Notes" you have other considerations. Take a control Voltage of 1 volt
>> per
>>> Octave from 0 - 10v. In this case Each Volt represents 12 "Notes" for 10
>>> Octaves Or 12 * 10 = 120 distinct notes. An 8 bit converter has 0-255 as
>> the
>>> output or 256 "steps" 256/120 = 2.133 in other words it is a mismatch.
>> you
>>> need to match the 120 notes to "steps" So you can set it us to use 240
>> of
>>> the 256 steps with 16 "steps" unused. In other words Using a vref+ of 5v
>> and
>>> a vref- of 0v you want 10v in to result in the converter outputting
>> "Step"
>>> 240. Each Step of the A to D is 0.01953125 volts, we want 240 of these =
>>> 4.6875 volts, So the input to the A to D should scale the 10volt input
>> at
>>> 4.6875/10 or 0.46875 .
>>> If the D to A is also using vref+ 5v and vref- 0v we need to do the
>> reverse
>>> to scale back up to 10 volts 10/4.6875 or 2.1333...
>>> I am just about to tired to think but I also believe that we have at
>> this
>>> point centered the "Notes" on the Step transitions, we really want them
>>> centered between the transitions, so as part of the Front end (A to D)
>> after
>>> the scaling we need to ADD 1/2 of a Step to the Voltage into the
>> Converter,
>>> or 0.01953125/2, 0.01v is close enough, and coming out of the Back end
>> (D to
>>> A) we need to SUBTRACT 0.01v before scaling the voltage back up.
>>>
>>> I hope this helps clear things up and not create total confusion.
>>>
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: synth-diy-bounces at dropmix.xs4all.nl
>>> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Dan Snazelle
>>> Sent: Wednesday, May 13, 2009 10:39 PM
>>> To: sdiy
>>> Subject: RE: [sdiy] AD/DA schematics? quantizers,etc
>>>
>>>
>>>
>>> ok
>>>
>>>
>>>
>>> i feel like a fool
>>>
>>> in all my reading and testing today i had somehow missed the fact that
>>> on an ADCchip, the vref cant go below grnd (or not much below)
>>>
>>>
>>>
>>> so i am confused. usually when i see a - sign i think of putting the
>>> negative rail. but in this case it seems you pick a top voltage and a
>>> you pick a bottom but that has to be within 0-vref
>>>
>>>
>>>
>>> is this correct? and the vcc is always 5volts?
>>>
>>>
>>>
>>> how high can the vref be?
>>>
>>>
>>>
>>> a few people have mentioned that for cv, i want a 10v vref.
>>>
>>>
>>>
>>> would a high vref be useful for audio as well? or a lower vref useful
>> even?
>>>
>>>
>>>
>>> thanks
>>>
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