[sdiy] Waveform/source mixers in classic polysynths

[Mattias Rickardsson]

Audio mixing takes signals of very different input levels and set them to
quite different output levels. A huge gain range is needed.

Synth waveform mixers, on the other hand, take signals of a well-known and
constant amplitude and very often set them to almost the same amplitude
into a filter. A small gain range is needed, and it's even good to have the
higher gains taking up most of the potentiometer range.

I guess that's why they differ in this regard. :-)

/mr




Den 5 okt. 2017 11:16 em skrev "Richie Burnett" <
rburnett at richieburnett.co.uk>:

> I've noticed this too Tom, and am interested to hear people's comments.  I
> have no idea why linear pots are used in synths to mix oscillator volumes
> instead of the more usual log taper for audio mixing!
>
> -Richie,
>
>
>
> -----Original Message----- From: Tom Wiltshire
> Sent: Thursday, October 05, 2017 9:29 PM
> To: *SYNTH DIY
> Subject: [sdiy] Waveform/source mixers in classic polysynths
>
> The accepted wisdom is that audio mixers should use a log response rather
> than linear response. Audio mixers are usually equipped with log pots for
> this reason.
>
> However, many polysynths have a waveform or oscillator/noise source mixer
> which usually uses linear control. Is there any reason for this?
>
> Is it just that it was simplest when the obvious VCA to control a source’s
> level ahead of the filter was based on an OTA, which has a linear response?
>
> Are there any examples of classic synths where this is *not* the case, and
> the waveform/source mixing is done with an audio/log response?
>
> Background: I’ve been looking at old schematics again, for the Prophet 5
> (learning from the masters!). I suppose there’s an outside chance they did
> a Lin/log conversion in the software before they sent the CV out, but I
> seriously doubt it.
>
> Thanks,
> Tom
>
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