Z-machine sound

[fredrik (Fredrik Ramsberg)]

Z-machine sound seems to be a bit magic, and I’m not sure the specification is complete. Some games loop, and the interpreter should just know which. But in z5 the sound_effect opcode can also specify looping. Can there still be sounds that will loop even without this being specified with the sound_effect opcode? And there’s one channel for music and another for sound effects. Was the music channel used in any of the Infocom games? Is all music repeating?

Is there anyone here who has added sound support to an interpreter and can tell me about some of the pitfalls?

Any additional information (or links to such) about how to make sound work correctly for the Z-machine are appreciated too.

[eriktorbjorn (Torbjörn Andersson)]

@fredrik

Was the music channel used in any of the Infocom games?

Wasn’t music something that was added after the demise of Infocom? The Z-Machine 1.1 standards proposal [1] it says that

The Blorb specification effectively revised Standard 1.0, as follows:

“Sound” is split into two classes - “music” (eg Blorb SONG and MOD) and “effects” (eg Infocom .SND or Blorb AIFF).

The Blorb specification says that SONG is deprecated, and I think MOD handles looping all by itself?

The only thing I’ve ever seen about music in Infocom adventure was the back of the Journey box, where it says that “Color graphics and theme music bring the action to life as the tale unfolds on your screen.” But no one - not even Marc Blank - seems to know what that was about.

(The link to the draft specification, or at least an earlier version, worked for me without having to use the Wayback Machine, but it stopped working for me while I was writing this.)

[1] Wayback Machine

[StJohnLimbo]

I haven’t really delved into interpreter development, so I don’t know if it’s going in the direction you’re looking for, but I remember reading about @DavidG implementing sound support in Frotz.

Here are some links to threads which contain further links:

The Lurking Horror source code loop handling

I’m looking at the ZIL code that handles the audio in The Lurking Horror, trying to work out how it handles the looping sounds. The interpreters that currently support sound effects in The Lurking Horror, Frotz and Bocfel, both have a hard-coded list in the source of the sound effects that should loop. But looking at the code, it seems that the special handling of the looping effects (S-DRONE, S-ATTACK, S-PSYCHO, S-MONSTR, S-VOICE, S-ZOMBIE, S-CRETIN) is in the game code rather than built into …

Lurking Horror on a HiDPI Mac with sound effects

I had that audio code MIT-licensed so that it could readily be used in non-GPLed terps. I’ve been planning to add it to GlkTerm, but that got backed up behind some other enhancements that haven’t yet been pulled in.

Kickstarter for full audio support for Unix Frotz

I’ve decided that I need to enlist some extra help to get audio support finally completed and working correctly and efficiently in Unix Frotz. My audio programming skills are not as good as I’d like, so I found someone who can do it for a fee. That someone is Mark D McCurry (fundamental-code.com/). To pay for this, I’ve created a Kickstarter campaign. This is intended to raise the $600 that Mark has asked for to reimplement audio support correctly. The target amount is $700 to cover overhea…

[fredrik (Fredrik Ramsberg)]

This is most helpful, @eriktorbjorn and @StJohnLimbo . Thank you!

[DavidG (David Griffith)]

Audio was done by Infocom only for “Lurking Horror” (only for Amiga) and “Sherlock” (Macintosh and Amiga(?)). The audio was in the form of uncompressed samples.

[cas (Chris Spiegel)]

@fredrik

Some games loop, and the interpreter should just know which. But in z5 the sound_effect opcode can also specify looping. Can there still be sounds that will loop even without this being specified with the sound_effect opcode?

Yes; the Infocom sound format included a flag meaning “loop forever”. Blorb files have a looping chunk which provides the same information. With this, interpreters shouldn’t need to have knowledge of which samples to loop in the Lurking Horror (which is the only place this “auto-looping” is used, as far as I know).

Is there anyone here who has added sound support to an interpreter and can tell me about some of the pitfalls?

Dealing with the Lurking Horror hack (described in the remarks of §9 of the Standard) is a bit annoying.

One interesting thing I found is that there is a sequence that goes something like this:

@sound_effect 11 2 8
@sound_effect 16 2 8
@sound_effect 16 3

Which is to say, start sound 11, start sound 16, stop sound 16. This is one of the reasons for the “queued sounds” hack: sound 11 needs to play once, so sound 16 must be queued up. But the last instruction there stops sound 16. So, depending on how you implement things, you’ll get a stop request that comes in while sound 16 isn’t running. No big deal, maybe, because you want to hear sound 16 anyway. But sound 16 is marked as a looping sound, so unless you handle this somehow, you could end up with sound 16 going forever (since the “stop” request was too early).

I also decided to not bother with checking “is this the second sound effect that happened since the last user input” (which is a proxy for figuring out whether there were two successive @sound_effect calls that need to be spaced out), but instead I check for whether the game is The Lurking Horror, and if the sound effect is 9 or 16, since these are the two cases where the sound needs to be queued. The end result is effectively the same, but only applies to one game, whereas implementing the Standard’s recommendation applies to all games.

[DavidG (David Griffith)]

You’re touching on another audio pitfall there. In Lurking Horror, there are a few places where multiple samples are fired off in quick succession. The timing assumes an Amiga 1000. For a modern terp on a modern host, this is too quick and so some samples stomp on others. I have been able to mitigate some of this in Frotz and am working on the rest.