DAC & Hz & Bitrate (??)

[mrapoc]

Hey guys

I am really struggling to answer these two questions:

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[FONT=&quot]For digital to analogue conversion further explain:[/FONT]

[FONT=&quot]How the sample resolution (bitrate) affects the converted signal[/FONT]

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[FONT=&quot]How the sampling frequency (Hz) affects the converted signal[/FONT]

I would have thought it would have been analogue to digital as I could write about the sampling rate/losing quality etc. as the digital signal literally cuts fidelity off (lessoning with a great bitrate).

Is it a mistake or am I looking at it wrong?

 

[Rastalovich]

Best thing to do to wrap ur head around it is to get some free audio conversion software, that shows waves especially, and watch what changing those factors does to the waveforms.

Or to keep in with the questioning, what the limitations can be.

 

[DeMoB]

Surely it's the same problems but just amplified by going back to analogue again.

If you've cut the data out by using a low bitrate going to digital, then going back to analogue is going to leave you with the quality issues still.

Dan

 

[mrapoc]

Ahh cool

What about frequency?

 

[DeMoB]

Wikipedia says:

Maximum sampling frequency: This is a measurement of the maximum speed at which the DACs circuitry can operate and still produce the correct output. As stated in the Nyquist–Shannon sampling theorem, a signal must be sampled at over twice the frequency of the desired signal. For instance, to reproduce signals in all the audible spectrum, which includes frequencies of up to 20 kHz, it is necessary to use DACs that operate at over 40 kHz. The CD standard samples audio at 44.1 kHz, thus DACs of this frequency are often used. A common frequency in cheap computer sound cards is 48 kHz – many work at only this frequency, offering the use of other sample rates only through (often poor) internal resampling.

So the sampling frequency rate dictates the frequency range of the output signal.

Dan

 

[mrapoc]

ok i think i answered it to an acceptable level now

For digital to analogue conversion further explain:

How the sample resolution (bitrate) affects the converted signal

The bitrate of a signal affects the converted signal as it takes effect on the signal previous to being converted. A digital signal with a low bitrate (such as an mp3 file) will sound “worse off” than a high bitrate file. This does depend on the listener (I cannot stand anything below 192kbps bitrate but cannot hear the difference of anything above – this also depends on equipment in use). So for example, if the digital signal has a low bitrate before being converted, it already sounds “bad”. Convert this to analogue and the analogue signal will also sound bad (assuming it is an audio signal) or be less accurate in the readings it hopes to carry. To conclude, the bitrate needs to be of a high enough value for the converted analogue signal to be up for whatever job it is designed for.

How the sampling frequency (Hz) affects the converted signal

The sampling frequency will dictate the frequency range of the converted signal. A low sampling frequency will bring about problems with the converted signal as aliasing which will add noise and other inaccurate reproduction of the previous sound state. A higher frequency will mean a more accurate conversion as frequency is the number of times the signal is sampled and stored. Although for such signals as a speech recording, not many frequencies will be necessary when compared to the latest techno release so a lesser frequency can be used. If a lesser frequency was used for something like techno, ranges of the track would literally not be included or included in a low quality state.

 

[DeMoB]

Just wondering what are these questions from/for?

In your first answer you've said what happens but not why, and I think they'll probably be looking for that too.

And in the second section, expand your first statement that the sampling frequency needs to be double the desired output frequency. Again I think they'll probably want why, but only knowing what I've read on wikipedia, I'm afraid I don't know.

Dan

 

[mrapoc]

for my college assignment on data types and signals.

we shall see tomorrow ill ask the tutor if its enough

but yeh i cud easily put that in

cheers

ill try repping you but it will probably go a bit craaaazy again

 

[DeMoB]

I'm already glitched and repp'd out, but I'm all for breaking the system some more, so repp away

Dan