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

[cheater00 .]

On Wed, Nov 6, 2013 at 12:28 PM, Tom Wiltshire <tom at electricdruid.net> wrote:
>
> On 6 Nov 2013, at 11:03, cheater00 . <cheater00 at gmail.com> wrote:
>
>> On Wed, Nov 6, 2013 at 11:44 AM, Tom Wiltshire <tom at electricdruid.net> wrote:
>>> The average human isn't going to hear much, if any, difference between 12, 16 and 24 bit DACs if the sample rate is reasonably high.
>>
>> I would only be happy to make such a statement in the case of an
>> oscillator signal, which due to its very correlated power is going to
>> do funny things to our auditory system.
>
> That's the situation we're talking about, and the situation I made the statement about!
>
> Justin's case was specifically an oscillator, and he didn't even mention wanting level control done digitally, so I assumed we'd be using the full bit depth/SN ratio and outputting signals at full volume. Similarly, I assumed that we've got one DAC outputting one signal - this is a long way from sending a full mix of many instruments through one DAC. I wasn't recommending using a 12-bit DAC for mastering your DAW or anything like it!

I know you know - I was not sure if Justin knew.

>> On Wed, Nov 6, 2013 at 11:59 AM, Richie Burnett
>> <rburnett at richieburnett.co.uk> wrote:
>>> save 24-bit for something like a synth that has to output 32 voices, each made of 4 oscillators all mixed together, with envelopes etc. The extra quantization levels are really useful here!
>>
>> I seriously doubt 24-bit D-A is within the reach of any synth
>> designer. Or even 22-bit. Not even Yamaha would bother.
>
> The DAC chips to do it are easily and cheaply available. Whether the analog side lives up to the promises made by that incredible S/N is a different story. But Richie is right - at least if you've got that much resolution, you can add a load of waveforms together without having to lose bits off the bottom, even if some of that might get lost in the noise floor.

We agree again. Except I'd be weary of DACs that say they have "24 bit
output" - tests I've seen show they're often missing a bit or a few.
Maybe the DAC really does generate 24 bit output, except it's already
degraded at the bond wire. But even with the semiconductor company
outright lying we're dealing with more issues on the analog side than
digital. The 21st bit is ~ 0.00000048 V, or ~ (-126) dBV. You're lucky
to find a synth with -90 dBV self-noise, which is the 15th bit. That's
9 bits going to waste.

(I might be off by a factor of two in the conversions from bit number to dBV)

Cheers,
D.