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Old 01 December 2013, 12:32   #23
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Join Date: Jun 2010
Location: NL/PL
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Originally Posted by john1979 View Post
Just wondering but why did the hardware designers even consider cutting this frequency sloping downwards?

Any noise above 21khz would have been inaudible.

Most of us would struggle to hear anything above 20khz, even when in our teens.
They must - first there is Nyquist requirement (reconstruction filter) second - Paula HW have implemented volume control as a 6bit PWM modulator that control output level - (my educated guess is that 8 bit DAC responsible for sample conversion precede 6 bit PWM volume control - 8 bit DAC produce reference variable amplitude/frequency voltage for 6 bit PWM switch - output is complex form where reference voltage i.e. samples are modulated by 6 bit PWM with fixed frequency approx 56kHz - cclk/64).

And perhaps above 21kHz things are not audible but spurious modulation product can be hear in audio band without problem - intermodulation distortions.

once i've heard very good quality audio in demo - i don't remember for a name of demo but one part have sound where Janet Jackson samples was used, and graphically it was 4 wave spectrogram flying on screen - i was amazed how clear and good quality audio Amiga can produce - for modern wavetabe synthesis i think Amiga can produce sound quite close to HiFi average user standards - Amiga limitation are slow CPU and lack of DSP capabilities - with decent DSP Amiga audio quality can be more than HiFi (beyond CD dynamics).

Originally Posted by mc6809e View Post
The "grittiness" of the Amiga's sound comes from all these additional harmonics that are produced as the output jumps from one value to another. The more slowly the waveform is output, the more additional harmonics appear in the output EVEN IF THEY WEREN'T PRESENT IN THE ORIGINAL SAMPLE.
"Grittiness" means only that original audio was sampled without Nyquist criteria i.e. sample rate was to low when compared to sampled frequencies - probably antialiasing filter was not enough efficient or algorithm used for sample rate conversion not particularly good - Amiga is very slow CPU - most of algorithms used by Amiga to perform audio processing are very simple and not particularly sophisticated.

For example sample rate conversion quality of various program can be compared on .
Good algorithms are available but they require very high processing power not avaiable not even 10 years ago thus 30 year old Amiga can't be even matched with this.
From Amiga perspective it will be useful to have similar functionality as join sprites i.e. form from one twice higher speed channel from two channels. It is a bit sad that it was not designed in that way but still not bad for 30 year old audio.

Last edited by pandy71; 01 December 2013 at 12:49.
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