Amiga soundcard Prelude vs Prisma?

[matt3k]

Hi All,

I am tempted to pickup either a Prelude with Mpegit or the new Prisma.

I have heard that the Prelude can use more sound programs, what would be the benefit?  Is this a function of AHI or a direct call to the card?

Seems like the Prisma will play newer file formats but won't have AHI for a bit.

What programs can the Prelude use beyond the Prisma?

Not much of a gamer, but which is better for games?

[Matt_H]

Given that the Prisma isn't available yet, I hesitate to suggest one way or the other. I think most of the Prelude's power and versatility comes from AHI. The Prisma will have a much more powerful processor, but if it doesn't have AHI I think its utility will be limited...

[spirantho]

For full AHI I would recommend the Prelude.
However, for compressed audio (and games which use compressed audio for music streams), the Prisma is probably the way to go.

[Matt_H]

Ian, can you tell us more about the Prisma's software? I think there's still a lot of confusion as to how that will work (well, on my part at least ). How will programs take advantage of the Prisma?

[matt3k]

Ian, can you tell us more about the Prisma's software? I think there's still a lot of confusion as to how that will work (well, on my part at least ). How will programs take advantage of the Prisma?

+1

[spirantho]

The aim is to give the Prisma a limited AHI device. It will always be limited because it's not really a sound card, it just happens to support uncompressed audio.
The software is centred around prisma.library - a library of easy-to-use functions such as "PlayFile()" and "PlayMemory()" - I like to keep things as simple to use as possible for the programmer.
There is also an MHI device for AmigaAMP, though AmigaAMP only supports MP3 files. Any other software using MHI should therefore be able to use it. Hopefully they'll one day add support for parsing OGGs and FLACs etc. too, but we're going to release it with a playing GUI in the meantime.

As there's no real standard apart from MHI, we can't really offer compatibility with other hardware decoder cards for apps without MHI (making an emulation library of the Prelude etc. may be possible but it would take a while and I'm not certain it's worth it).

Anything you're not sure about specifically? Happy to help.

[matt3k]

Thanks for the great description!

I'm looking to primarily use this in a HIFI system for listening to audio.  

How will the quality compare with a Prelude for that?  The chip will be faster than the Mpegit, but will the quality output to a HIFI be comparable?

[spirantho]

Thanks for the great description!

I'm looking to primarily use this in a HIFI system for listening to audio.  

How will the quality compare with a Prelude for that?  The chip will be faster than the Mpegit, but will the quality output to a HIFI be comparable?

Then you want the Prisma.  And don't use MP3s if you can help it, use OGG or FLAC... better quality. If you really want to use MP3s though, you can use Mpeg 2.5, and you can use the higher bitrates.
Your HiFi does have S/PDIF for digital audio, right...? You don't need it, but it will help with quality.

[matt3k]

Thanks!

I'm using lame to encode the MP3's with the Insane setting for quality on my Powerbook running MOS and Flacapella, but I can switch if I can hear the difference.  These sound brilliant on my Delfina Plus using amplified speakers with a base box.

This card will go into my old school HIFi, which is RCA jacks for the input.

[Matt_H]

So it sounds like it's AHI for basic audio out, and then prisma.library for the complex decoding?

[spirantho]

Basically, yes. The Prisma is a decoder really, it just happens to be able to play spot effects - but only one per channel at a time. AHI does support software mixing, but it will be slower.

What you can't do on the Prisma is play a music in the background and then play spot effects on the same channel - so you're limited to using another sound source like Paula for spot effects (though you don't really need CD-quality blood splattering sounds or whatever )

The Prisma is first and foremost a music card - the real advantage I reckon is that it allows us to use really good quality streams on a humble not-very-expanded Amiga, even a 68000-based one. I can't think of any other way to play heavily compressed lossless or high quality audio on a low-spec machine, and I think even a faster 68K Amiga would struggle normally with the high bitrate MP3/OGG/FLAC streams.

I can't say what the quality is like compared to a Prelude because I don't have one, but I do know it sounds good and the background noise level is notably less than my PC.
For what it's worth I do tend to notice when something doesn't sound good (I'm the sort of person who spends far too much on his vinyl ), and it does sound pretty fine to my ears.
I have high hopes (and I don't just mean Bruce Springsteen's latest album, but that may be played too) for FLACs played through the S/PDIF digital output .

[Matt_H]

Thanks for that explanation! I guess, concept-wise, it doesn't sound like it's vastly different from a Delfina or another of the old soundcards with a hardware MPEG decoder (but without recording ability?).

I think I mentioned it when the board was announced, but I would like to suggest again an mpeg.device compatible software interface at a later date/in addition to/instead of an MHI driver. I don't think MHI was used for anything other than AmigaAMP, whereas there are a few more programs that can use mpeg.device (including MHI). I just discovered this one which sounds really cool and could open up the possibility of hardware decoding to a lot of old software.

[spirantho]

It does have recording ability, but only from line-in or mic in.

I'm not sure about mpeg.device - maybe later in its lifecycle.... but if it was that suitable they wouldn't have invented the MHI interface. I may look into it in future.

The real advantage is the support for so many formats, I reckon.

[ognix]

Hello!
Ian, thanks for the explanations.
Just another question: from what you told is not possible to mix together two tracks, for example, unless you previously mixed audio them into a stream via main processor, right?

I'm asking this especially thinking about some a possible use inside audio mixing applications (since the DSP).

[spirantho]

I don't think the Prisma would be suitable for mixing, I'm afraid. You need a proper dedicated DSP rather than a decoder for that - and I think the latency would be too high on the Prisma if you want things to mix properly. To mix two tracks you'd have to "decode" a pre-mixed WAV.