FW: MIDI2CV alternatives (was: Re: [sdiy] Newbie alert :-))

[phillip m gallo]

Marc is correct.  8 bit converters only need be damn accurate and then drive
damn accurate VCO's/VCF's.  As a mature category of products 8 bit accuracy
is easily obtained at low cost.

Also if the MIDI2CV device is going to also provide for pitch bend and other
modulation it is  best to provide a second 8 bit converter to emit this
control voltage (either weighted and summed at the target or within the
MIDI2CV itself).  Pitch Bend is actually more challenging than Note ON/OFF
as this is a 13 bit + sign value.  If pitch bend is held to 2 1/2 semitones
8 bit conversion performs smoothly, larger increments can produce
progressively audible staircasing.

If the VCO is not accurate however, a single 8 bit converters may not have
the resolution to correct it across 10 octaves.  This is where "wider" DACs
have advantage, many  VCO designs are not really up to 10 octaves of
accuracy with most of the error being found at the extreme ends of a 10
octave freq. span. In these cases you find 12-14 bits provides enough
resolution to correct these.  The equivalent of this resolution can be
obtained using summed and weighted 8 bit DACs.

regards,
p


-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of marc bareille
Sent: Wednesday, October 06, 2004 6:38 AM
To: Paul Maddox
Cc: Synth-Diy
Subject: Re: MIDI2CV alternatives (was: Re: [sdiy] Newbie alert :-))


Hello

> nice, but only 8 bit DACs, given the non-linearity errors you get with
> 8 bit
> DACs( 1 or 2 bits) you could have problems with pitch tracking over a
> large
> range.
>
>
>
"Only 8 bits DAC" for sure it is ... but  without any trouble on over 8
octaves range  in 1V/Oct !!!   Really i love you 8 bits detractors but
you should try first may be ...  You will be surprised to discover that
if your synths an the MV interface are correctly trimmed 8 bit DACs are
sufficient enough  for 1V/Oct scales. Considering the wide number of
those interfaces i have builded ,installed in vintages synth, and the
impressive number  of feedback emails of happy MCV628/876  builders  i
told to myself that if it had a linearity problem , i should seen it as
well as other ppl ..

I admit 8 bit is a bit short to finely emulate  V/Hz scale ... That is
why  i am actually testing the 16 bit  mode with the same 8 bit hardware
.... It will allow management of Pitch Bend too  and hi accuracy V/Hz
obviously ... Note to implement  this mode on any MC just  one more
extra resistor is required  on the MCV  pcb !!!  :)

I am actually writing page for a massive upgrade of the site ... So be
preprared to see in coming days the MCV876 , now polyphonic 2 to  4 CV
voices , with Midi clock integrated and many many other cool  features
inside like velo triggers etc etc ... the MCV firmware is now V2.01...

Best Regards,

Marc B.



Paul Maddox wrote:

>Hi,
>
>
>
>> MCV628, MCV876 also should be checked!
>>
>> http://m.bareille.free.fr/mcv628/mcv628.html
>> http://m.bareille.free.fr/mcv876/mcv876.html
>>
>>
>
>nice, but only 8 bit DACs, given the non-linearity errors you get with 8
bit
>DACs( 1 or 2 bits) you could have problems with pitch tracking over a large
>range.
>
>Paul
>
>
>
>
>

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