[sdiy] DACs on-board 12 vs external 16 vs 24 bit

cheater00 . cheater00 at gmail.com
Wed Nov 6 17:04:42 CET 2013


Hi Neil,

On Wed, Nov 6, 2013 at 5:00 PM, Neil Johnson <neil.johnson71 at gmail.com> wrote:
> Pete Hartman wrote:
>> I'd be interested to hear about those omissions to learn more....
>
> One is that, as far as I can see, it fails to explain *why* the
> reference for 0dBu is 0.775V.  Yes, I know the answer, but it is not
> clear on that page.
> Also, a minor irk, is that when talking about dBm they say "Typically
> the impedance (load) is 600 ohms" -- well, not in my experience in RF
> where dBm is very commonly used, and impedances are typically 50 or 75
> Ohms.


I've had a feeling you'd bring up the dBm calculations. AFAIK dBm is
normally specified into 600 Ohm, unless specifically noted otherwise.
However, even with 600 Ohm meters, the impedance dissipating the power
is denoted. The manual always has that info.

600 Ohm is the typical value for dBm as used in audio engineering, and
I have a feeling that this page is focused specifically for that. No
RF concepts are mentioned.

I too think it would be a good idea for them to mention where the dBu
and dBV references come from.



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