[sdiy] SSM2164 panning curve

Derek Holzer derek at umatic.nl
Fri Jul 24 19:02:31 CEST 2009 

HI Jerry,

that's not a bad idea. By "curve adjustment", do you mean a voltage 
offset, or something more involved?

D.

Jerry Gray-Eskue wrote:
> <<It always felt like
> it had a "dead spot" in the middle where it wasn't as loud as it should
> be.>>
> 
> You may be getting too much drop off at the center, it could be illuminating
> to check out what your actual levels are at center and full off to one side.
> This setup may just need a re-curve of the control voltages to kill the dead
> spot.
> 
> If nothing else dinking about with the voltage curves may help you find the
> levels you want to build into your new module. You may also want to put
> curve level adjustments in anyway, so you can compensate for non ideal /
> mismatched speaker and acoustic setups.
> 
> - Jerry
> 
> 
> 
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Derek Holzer
> Sent: Friday, July 24, 2009 9:40 AM
> Cc: Synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] SSM2164 panning curve
> 
> 
> One reason I started this thread was that I built a voltage controlled 4
> to 1 mixer right from the schematic in the SSM2164 spec sheet and
> controlled it with a Doepfer A-174 Joystick module. It always felt like
> it had a "dead spot" in the middle where it wasn't as loud as it should
> be. A slightly different application than quadraphonic panning, but this
> experience is still in my mind as I plan out this new module.
> 
> D.
> 
> Jerry Gray-Eskue wrote:
>> <<In the dead center, both channels will be mixed equally at some level
> less
>> than unity, but which when added gives the same loudness as a single
>> signal at unity.>>
>>
>> Assuming an ideal speaker setup (equal distance from listening point and
>> room acrostic matching), yes with this setup the joystick will "move" the
>> quadraphonic sound in direct relation to the joystick position.
>>
>> I believe the "Magic" level is 1/2 the power (~= -3db) in center position
>> which is why one of the "panning laws" uses -3bd for the center position.
>>
>> - Jerry
>>
>> -----Original Message-----
>> From: synth-diy-bounces at dropmix.xs4all.nl
>> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Tom Wiltshire
>> Sent: Thursday, July 23, 2009 1:34 PM
>> To: Derek Holzer
>> Cc: synth diy
>> Subject: Re: [sdiy] SSM2164 panning curve
>>
>>
>> Derek,
>>
>> Ok, cool. Now I'm with you. I think. Famous last words.
>>
>> Basically you want the sum of the outputs to remain constant. I'm not
>> bang up to date on the latest in the panning law debates, but I
>> understand that some people prefer the "equal power" version whilst
>> other people go for "equal level" or some such distinction.
>>
>> Let me just think this through aloud...
>> Presumably the X-axis and the Y-axis are identical? So we can look at
>> one of them independently of the other. So if you solve the problem
>> for one direction, you just repeat it for the other.
>>
>> On that basis, let's have a look at the Left/Right axis. On the hard
>> left side, you'd want only LHS signal, at unity gain. On the hard
>> right, you'd want all RHS signal, again at unity. As you move away
>> from these positions, the volume of that channel decreases whilst the
>> other increases, following the log response curve of the VCA. In the
>> dead centre, both channels will be mixed equally at some level less
>> than unity, but which when added gives the same loudness as a single
>> signal at unity. Am I still on the right lines?
>>
>> Given that the SSM2164 does the complicated linear CV to logarithmic
>> response part for you, I'd have thought you just want a circuit that
>> gives you a linear voltage for the CV, say 0V (unity) to +4V (>120dB
>> attentuation). This needs to be inverted and offset for the opposite
>> VCA, to give 4V to 0V instead. This isn't difficult (a lot simpler
>> than that electromusic schematic). The joystick pot can provide one
>> CV directly (with a bit of tweaking) and then the opposite one needs
>> an inverting op-amp mixer, fed with the CV and an offset voltage of
>> -4V. And then same again for the other channel.
>>
>> Hope this helps,
>> Regards,
>> Tom
>>
>>
>> On 23 Jul 2009, at 14:21, Derek Holzer wrote:
>>
>>> Hi Tom,
>>>
>>> sorry don't have an image right now, but let me try someone else's
>>> explanation:
>>>
>>>> Some words about panning and crossfading:  If you simply have two
>>>> VCAs connected together such that varying the control voltage
>>>> brings the gain on one up and the other one down, you have a
>>>> rudimentary panner, but the panner has a problem.  At dead center
>>>> (both VCAs equal), the loudness will be less than full right or
>>>> full left.  You need some flattening of the response curve to make
>>>> this complete.  The Serge VCAs provide this equalized left-center-
>>>> right response curve, so panning sounds fairly natural.
>>> From: http://www.serge-fans.com/wiz_vca_mix.htm
>>>
>>> Does that explain my idea a bit better? At center position, all
>>> channels should be at unity, and should never get louder than that.
>>>
>>> D.
>>>
>>> Tom Wiltshire wrote:
>>>> Derek,
>>>> I'm afraid I don't understand what you're trying to do. I need to
>>>> see more diagrams for my visual head to get it. So long as you're
>>>> clear about it, that doesn't matter.
>>>> However, I have played with the SSM2164. 15V is too much for the
>>>> control port. The datasheet gives the CV response as -33mV/dB.
>>>> Hence you need 3.3V for fully off -100dB, and -0.66V for 20dB
>>>> gain, with 0V giving you unity gain. I don't know of a way to set
>>>> the SSM2164 up for attenuation only. You just make sure that you
>>>> only have positive control signals. I don't think just a simple
>>>> diode would work that well, since the diode won't conduct until
>>>> the CV is significantly negative, which isn't what you want. You
>>>> could modify the op-amps in the Electro-music schematic to
>>>> precision half-wave rectifiers, which would give you a more
>>>> accurate result.
>>>> Regards,
>>>> Tom
>>>> On 23 Jul 2009, at 11:31, Derek Holzer wrote:
>>>>> I've got a hopefully simple question about using the SSM2164 as a
>>>>> joystick controlled quadraphonic spatializer/panner. I have been
>>>>> looking at Marc Bareille's Quad VCA/CV-Mixer as a good model for
>>>>> this project:
>>>>>
>>>>> http://m.bareille.free.fr/modular1/quadvca/quadvca.htm
>>>>>
>>>>> with some additions for the joystick control:
>>>>>
>>>>> http://electro-music.com/forum/viewtopic.php?t=24705
>>>>>
>>>>> My concern is this: when the joystick is it dead center the gain
>>>>> on all channels should be unity. However, for this particular
>>>>> gain/panning curve I don't want more than unity gain, only
>>>>> attenuation. I am aware that this nulls the effects of half the
>>>>> range of the joystick... however from what I have read this is
>>>>> the panning curve used by the Serge and Buchla spatializers, and
>>>>> it makes sense acoustically to me.
>>>>>
>>>>> So let's assume that set up the SSM2164 as in the datasheet,
>>>>> where 0V is unity and minus voltage is attentuation. And I wire
>>>>> up my joysticks as voltage dividers between +15 and -15 (or
>>>>> should it be +/-5V?). But since I don't want any amplification, I
>>>>> use a diode to block the positive voltage coming from the
>>>>> joysticks, making sure the diode is rated not to break down
>>>>> anywhere near 15V (or 5V?). Am I on the right track? Or is there
>>>>> a way to set up the SSM2164 itself so that it only attenuates?
>>>>>
>>>>> Thx+best!
>>>>> Derek
>>>>> --
>>>>> ::: derek holzer ::: http://blog.myspace.com/macumbista :::
>>>>> http://www.vimeo.com/macumbista :::
>>>>> ---Oblique Strategy # 52:
>>>>> "Do nothing for as long as possible"
>>>>> _______________________________________________
>>>>> Synth-diy mailing list
>>>>> Synth-diy at dropmix.xs4all.nl
>>>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>>>
>>> --
>>> ::: derek holzer ::: http://blog.myspace.com/macumbista ::: http://
>>> www.vimeo.com/macumbista :::
>>> ---Oblique Strategy # 107:
>>> "Look at the order in which you do things"
>>>
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
> 
> --
> ::: derek holzer ::: http://blog.myspace.com/macumbista :::
> http://www.vimeo.com/macumbista :::
> ---Oblique Strategy # 80:
> "Go to an extreme, come part way back"
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> 
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> 

-- 
::: derek holzer ::: http://blog.myspace.com/macumbista ::: 
http://www.vimeo.com/macumbista :::
---Oblique Strategy # 163:
"Turn it upside down"

More information about the Synth-diy mailing list