[arch-general] OT: [arch-dev-public] polkit package upgrade patch

[Mauro Santos]

On 12-08-2012 18:38, Ralf Mardorf wrote:
> On Sun, 2012-08-12 at 18:09 +0100, Mauro Santos wrote:
>> On 12-08-2012 17:11, Ralf Mardorf wrote:
>>> On Sun, 2012-08-12 at 18:02 +0200, Tom Gundersen wrote:
>>>> The second case, where the total gain should be <0dB, I would have
>>>> thought intuitively that doing this purely in software (especially on
>>>> very faint signals) would be less ideal than doing it in hw (you'd be
>>>> throwing away the resolution, wouldn't you?), but I'll admit that I
>>>> don't have the experience to talk about that with any authority.
>>>
>>> It's a common misconception that keeping the level lower than 0dB would
>>> lead to less "resolution". It depends to the sampling rate and bit depth
>>> and less to the level control.
>>>
>>>
>>
>> Sampling rate would not matter to level discussions since it limits only
>> the maximum frequency that can be properly sampled or reproduced.
> 
> Agree, but it is also "resolution".

Of course it is also resolution, but we were discussion resolution
related to signal level, not temporal/frequency resolution.

>> For the same bit depth a lower playback output level will yield a lower
>> signal-to-noise or signal-to noise + distortion ratio, thus leading to
>> the same effect of having a DAC of less resolution playing at full
>> scale, so in a way you can say that for lower output levels you have
>> less resolution.
> 
> But the lower resolution doesn't become audible that easy, if the bit
> depth is high enough.

If you have proper electronics, for a higher resolution the noise floor
will be much lower than the minimum signal your transducer can play so
you can't possibly notice it. But use a low enough signal level followed
by amplification in the digital domain (without allowing it to saturate)
and you will tell the difference.

> It's better to keep the level within reason
> instead of 0dbFS. Even at 48 KHz 16 bit, headroom is better than maximum
> level.

Of course you should have some headroom, if you are sampling an analog
signal you can't know the maximum amplitude beforehand so you need some
headroom, it is however always advisable to use the highest input level
possible.

If we are talking about digital systems, you know exactly what the
maximum level is, if the DAC is good and all the following electronics
have been properly engineered you can't blame anything but yourself if
you get clipping after digitally "boosting" your signal.

> And if you use totally low bit sampling e.g. 2bit for the C64,
> you need to play with the level. Higher level doesn't mean better sound
> quality per se.

Again, for any given bit depth if you use a higher level you will get a
better signal-to-noise ratio.
Sounding better is a whole other story, that is a subjective measure
that is related to the human hearing system and is not easy to
quantify,it is related to how faithfully you can replicate a signal and
the C64 can't possibly be called a system designed to faithfully
reproduce sound.

-- 
Mauro Santos