4016, switching audio and VCO signals

[Arthur Harrison]

The CD4016 is a fine quad analog switch for many applications,
however, note that there is considerable on-resistance variation
that is signal-voltage dependent.  This is the characteristic that
inevitably leads to signal distortion in some audio (and other)
applications.  However, you may not notice this in your oscillator
application, since you are apparently commutating fixed voltages,
and these voltages may be "pre-distorted" to compensate for switch
resistance variations.

On the other hand, applying these devices in a music or voice audio
circuit _may_ introduce noticeable distortion depending on relative
impedances in the switch path.  Also, be aware of the charge injection
parameter for this device.  Such charge injection might cause audible
"pops" during commutation.  Even if charge injection were infinitesimal,
the rate of change, i.e., the abrupt switching action of such devices,
will most certainly cause a noticeable "click" during program transitions.
Also be aware of channel separation between switches in the same package.

The 4016 is very inexpensive, and manufactured by a number of vendors.
These are great benefits.  However, high-end audio switchers do not
generally
use them for the above-mentioned reasons.  Here's an alternative choice:
Analog Devices SSM2404.  A blurb with further links may be seen at:
http://products.analog.com/products/info.asp?product=SSM2404
This device incorporates a "ramping" technique to assure "clickless"
switching.

Aside from these application-specific audio switches, there are also a great
number of devices available with very low charge injection and essentially
"flat"
on resistance.  Both Analog Devices and Maxim are good places to start
looking.

-Art in thereminland

"If you met yourself, would you form a band and harmonize?"


-----Original Message-----
From: Mark Havard-Brown <mark at spooky-solutions.co.uk>
To: synth-diy at mailhost.bpa.nl <synth-diy at mailhost.bpa.nl>
Date: Monday, December 07, 1998 7:00 AM
Subject: 4016, switching audio and VCO signals


>All,
>
>Has anyone used these 4016 Quad Bi-Lateral Switches. I'd like to know if
>they are okay to switch audio, (the fact sheet on them says they will), but
>I'd rather hear it coming from someone who has used them. I'm looking at
>using them to construct complex oscillator shapes by switching voltages
>clocked via a counter. Could they be used in a MIDI controlled audio patch
>bay, or is the audio response poor if I were to switch CD quality audio
>signals through them.
>
>
>
>Mark.
>
>