Amiga sound playback routine/format questions

[bubblebobble]

Not that I know of.

It's all easily possible with the includes (ADPCM4 Codec, AHI Playback), but not with a 7MHz nacked Amiga.

I wrote a 14bit Audio output routine once for BlitzBasic in inline ASM. But I dont know if I have it still somewere. If you know how to deal with the Paula Registers, 14bit playback is not so hard to do. I also think that the ADPCM4 Codec (4bit per sample) I wrote is fast enough for 7MHz (depends on the Samplerate of course), but I think it would be quite busy then.

[bubblebobble]

@bloodline

You forgot to mention that the lower byte has to be shifted down 2 bits. This is where the 14bit comes into play. 64 is only 2^6. If they had made the volume control with a granulariy of 256 instead of 64, you could get 16bit playback.

Looseless goes not beyond 1:2 compression. But lossy ADPCM is cheaper to decode and at 8bit sounds pretty good (I cant hear a difference with HQ equipment). It still sounds acceptable at 4bit, but high frequencies get a little rough though.

We had this discussion once already:

PCM 16bit
ADPCM 8bit
ADPCM 4bit
ADPCM 2bit

Those are all plain .wav files, but have been encoded&decoded.

[bubblebobble]

As Britelite pointed out at boozembly, plain shifting is slightly wrong though. If you want "perfect" scaling typically you'll use a lookup table.

Sure, and if you want to do it really perfect, you do dithering.
But we are talking about a hack that adds two audio signals to resemble 14bit. Because the playback is far from beeing perfect/linear etc., the result is not perfect 14bit. I would say the noise from artefacts is somehow comparable with something like 12bit. So you do not really gain a lot from trying to be better than a simple shift, which is the fastest way to do it.

[bubblebobble]

> Yeah, I do get 3.3:1 compression in my Gita multimedia CD
This is probably due so relatively silent parts in the samples and/or the 8bit quantisation.
Try the same on some randrom music in 16bit. In average, you wont get better than 1:2 when you go loosless.
http://wiki.hydrogenaudio.org/index.php?title=Lossless_comparison

And Amiga_Nut needs something fast enough for a nacked A500 that should do some GFX in the meanwhile.

[bubblebobble]

If Paula is a 14bit DA Converter, what is the "calibration" for then?

As for th downsampling, this is another story, but can be done "offline". I used to do 44.1kHz with interrupt, but on a 68060.
With dithering I mean to reduce (or better mask, it is some kind of noise shaping) the audible quantisation noise. Just like dithering in images with low bit depth.