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Re: attenuator

I haven't done an exhaustive search recently, but in 
general the problem with these digital potentiometers is 
that they are just that - potentiometers, not the sort of 
attenuator one typically wants for audio work, which would 
allow setting any dB value with 1 dB resolution from 0 to 
100 dB or more.

If you search on "digital attenuator", be careful because 
the vast majority (maybe all) returns will be for microwave 
and other RF devices.  "Digital audio attenuator" gets into 
the proper frequency range, but the products typically 
don't have nice 1 dB steps... they have fine steps at high 
levels and coarser steps at lower levels.

Since you mention RS232 control, are you using "older" 
technology?  If you have a system with an old ISA data bus 
(pre-PCI), you can use an old ISA-bus Sound Blaster like 
the SB16 or AWE32 as an attenuator.  These had outstanding 
specs... *way* better than lab-type units of the day. They 
allowed 2 dB steps over a 138 dB range.  Even though the 
sound card sample rate was limited to 48 kHz, the frequency 
response attenuators alone on the SB16 were only 1 dB down 
at 60 kHz, -3 dB at 110 kHz.

You can see typical specs at

Best regards,

Bob Masta

On 17 Nov 2011 at 17:23, David Smith wrote:

> Pawel,
> There are hundreds of different "digital potentiometer" chips  
> available to do this.
> For example:
> Dual 8 bit digital potentiometer ,3 wire serial port, clocked  
> communications.
> Accuracy is typically specified in parts/million.
> You can use them directly on analog audio or use them to set gain of  
> amplifier stage.
> Communication software for this is trivial if you can flip a few bits  
> on a computer port.
> Dave Smith
> On Nov 17, 2011, at 3:40 PM, PaweÅ? KuÅ?mierek wrote:
> > Dear list,
> >
> > I was wondering if you know of any commercialbly available precise  
> > digitally controlled  (i.e., repeatable) attenuator with fast and  
> > quiet attenuation changing. Preferably, but not necessarily  
> > controlled via RS232.
> >
> > All suggestions welcome,
> >
> > Thank you,
> >
> > Pawel Kusmierek

Bob Masta
            D A Q A R T A
Data AcQuisition And Real-Time Analysis
Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!