Amiga audio capabilities

[Zac67]

Interesting - completely forgot about the AM/FM modulation capabilities - have they ever been used?

However, 14 bit playback isn't done with AM but rather two synchronized channels, one running at highest, the other at lowest volume. Due to the 6 bit volume resolution, they overlap 'in the middle' so two bits need to be eliminated. (You just put the high byte in the high channel, and for low byte you shift right two bits and then put it on the low channel.)

Using AM for high resolution playback is an interesting idea - it'd be a kind of highly dynamic compression that follows the wave level. But then again, each sample would only have 8 bit resolution even at highly varying volume levels.

Also, Paula's sampling speed isn't really limited to 28 kHz - but the DMA system is. On ECS with a increased scan rate or the - rarely used - PIO mode it can be much higher. Is that 1.7 MHz the maximum hardware sampling speed?

Just wondering - with 14 bit DAC resolution but 4x oversampling you could recreate the two dropped bits through PWM. E.g. an '030 with fast RAM should easily be capable of feeding Paula...

[Zac67]

Er, depends how it works.  If it's modulating the channel directly then yes it'll stay as 8 bit.  However, if it's modulating the volume of the channel (I assume it does this) then it'll effectively be 14 bit.

Yes, you're right. The volume knob just multiplies the 8 bit sample by something from 1 to 63 - which would be the same (depending on how exactly the volume works, of course).

Either way, it'd be interesting to compare them.

Sure, maybe someone will code something like that some day.

As I understand it's the maximum output speed from a pair of samples in a buffer, however it's not clear if you can update the samples any faster than the normal maximum playback rate - you might be able to get the CPU to write them but it depends on how faster the buffer updates.

Usually the DAC buffers are updated through DMA and the DMA update rate is limited to two samples per scan line (why this boils down to 28.8 kHz I don't recall, sorry), so you either raise the scan rate or 'manually' feed the buffers from the CPU (just update the buffer before the next sample is played back).

[Zac67]

On a side note, shouldn't it be possible to use the Copper in a low color mode to program Paula directly, and get 44 Khz, 14 bit stereo that way? The would really be cool

Yes, why not? Somewhat inefficient, but a cool idea, really!

[Zac67]

Usually the DAC buffers are updated through DMA and the DMA update rate is limited to two samples per scan line (why this boils down to 28.8 kHz I don't recall, sorry), so you either raise the scan rate or 'manually' feed the buffers from the CPU (just update the buffer before the next sample is played back).

Hmm - looking around in the manuals on hand, there's just one time slot per scan line per channel (4 in total). How does this yield 28.8 kHz sampling rate?

[Zac67]

Any choice for download it with plain windows xp?

http://www.itefix.no/i2/node/10650