Digital potentiometers why not more widespread...

[Bas Horneman]

Won't a digital pot be the ultimate in combination with a nice DAC?

Why are there no diy examples of these around?

Or are there?

Regards,
Bas

[A 8]

How do you figure it would be "ultimate" with a nice dac?

[Bas Horneman]

Since I suppose attenuation in the digital domain would do less harm?

[tiroth]

Edit: no, I disagree. Better to do only very small or no digital attenuation. Linearity will be much better.

[Christer]

Originally posted by Bas Horneman
Since I suppose attenuation in the digital domain would do less harm?

You will need a DAC with a much better dynamic range then, so
it seems a bit questionable. It also assumes all sources are
digital in order to make sense.

[tiroth]

If you want a digital pot just buy a sound blaster extigy and use the digital in and out.

[A 8]

Well, by doing it the digital domain you loose digital resolution and get more distorsion compared to analog attenuation on any level below 0dB.

[August]

Although I have a digital attenuation on my dCS DAC, I never use it because it decreases the overall resolution audibly.

In my opinion adding a good preamp is better than driving a poweramp directly with a digital attenuation in the DAC. YMMV.

[Bas Horneman]

Ok...that is settled .... digital attenuation sucks!

Thanks for all the contributions...

Cheers,
Bas

[dwk123]

Originally posted by Bas Horneman
Ok...that is settled .... digital attenuation sucks!

Thanks for all the contributions...

Cheers,
Bas

It may not be worth dredging up the details, but simply saying that digital attenuation sucks is way too simple.

It is probably true that for the 'typical' diy project, analog attenuation is easier/cheaper and likely to be better than digital attenuation. However, if you design and set up your system properly, digital attenuation *can* be essentially perfect. It's not all that easy to do, though.

Mathematically, digital attenuation is so close to perfect *provided you preserve 24 bit output* as to become an academic question - the distortion products will be 140dB down. However, in a real-world system the performance of the DAC is what limits the performance of a digital attenuation approach. Once you shift your signal down to where the the LSB of the input reaches the level of distortion and low-level nonlinearity of the DAC, you're to the point where you are distorting the signal.

With a modern high-performance DAC, you typically have noise/distortion/linearity performance down around -110 to -115 dB below full-scale. A 16 bit input from a CD has an inherent dynamic range of 96dB, so the first 10-15 or so dB of digital attenuation will be effectively perfect. HOWEVER, due gain mismatches between source and power amps, it is not unusual for a system to run with 5-10dB of attenuation even when playing loud, and 'typical' listening levels can easily be 20+dB down from full-scale, meaning that you are into the area where you are comprimising performance before you even start.

Of course, the noise floor and distortion profile of the power amp also come into things, but that doesn't change the fundamental issues, simply changes the boundary levels a bit.

So, all of this means that in most practical situations analog is the way to go. However, if you carefully design your system with the specific intent of being all-digital, you can build digital attenuation into the system without compromising it in any significant way.