It is currently Thu Nov 14, 2019 4:42 pm

All times are UTC - 7 hours

Post new topic Reply to topic  [ 4 posts ] 
Author Message
PostPosted: Mon May 20, 2019 10:04 pm 

Joined: Sat Apr 27, 2019 11:56 am
Posts: 34
I am getting a bit lost when trying to understand the tempo setting of the Taito audio engine I am working with. The things I have found out so far are:

    There is a byte in the header of every channel's data which specifies speed.
    This byte is usually 0x07. When I decrement this value the corresponding channel speeds up.
    Famitracker documentation states 150 bpm is the standard on NTSC APU's.
    Sheet music states my games main song is 120 bpm so I am guessing something changed along the way to accommodate this.
    The only store I see on $4017 is 0xc0 at the .nsf's entry point.

I am not sure how to confirm beats per minute given the game's songs I can play in nosefart. It would be a great start if I knew 0x07 was 120 bpm and 0x06 increased things to 150 bpm as some of the music I am attempting to port has sheet music listing 150 bpm. Is there some math I am missing which I can use to confirm these values? For example in the notes section for both the square and triangle waves I could pinpoint their delay register values and use f = CPU / ( (16 or 32) * (t + 1)) to confirm I had things right.

Any help is appreciated or if I've missed a forum post in searching let me know.

PostPosted: Mon May 20, 2019 10:20 pm 

Joined: Sun Apr 13, 2008 11:12 am
Posts: 8671
Location: Seattle
The standard Protracker terminology assumes 64 rows and four measures in a pattern, so one 16th note is one row. With the NTSC 60Hz timebase, and a "speed" of 6, this sets the 16th note duration to 100ms (6 ÷ 60Hz), a quarter note = 400ms, and (60 seconds/minute)÷(0.4 seconds/quarter note) = 150bpm.

Still assuming one row = one sixteenth note, you'd need a speed of 7.5 to get exactly 120bpm (120bpm = 500ms/quarter note = 125ms/sixteenth note; 125ms x 60Hz = 7.5). Some playback engines let you alternate automatically between 7 and 8; in other places I've seen the composer have a channel contain nothing but an endless stream alternating between setting the speed to 7 and 8.

PostPosted: Tue May 21, 2019 6:15 am 

Joined: Sun Sep 19, 2004 11:12 pm
Posts: 21688
Location: NE Indiana, USA (NTSC)
These are considered the "standard" tempos for sixteenth-note rows if your driver doesn't support in-between tempos:

900/5 = 180
900/6 = 150
900/7 = 128.6
900/8 = 112.5
900/9 = 100

Lidnariq is correct that some audio drivers can play at an in-between tempo, with one drawback being slightly uneven row lengths. I'm not familiar with what FamiTone2, GGSound, and classic era commercial games' drivers can and can't do tempo-wise, but Pently can hit any number of rows per minute, with a couple modes for making the tradeoff between even tempo and ability to hit all the in-between tempos.

Pin Eight | Twitter | GitHub | Patreon

PostPosted: Tue May 21, 2019 8:16 am 

Joined: Sat Apr 27, 2019 11:56 am
Posts: 34
Woah, these responses were quick and great. I went straight back to the .nsf and with a few changes confirmed a few things.

Due to a table of 8 values in one of the games looping note functions I erroneously thought 0x07 was the highest possible in my first RE pass. After seeing the previous two posts I tested out 0x08/0x09 and sure enough the tempo changes in the direction expected. This is a pretty basic engine based on most of my RE observations so I am fairly confident you guys' math is spot on and sheet music I found online is at 120 for convenience.

For reference on what threw me off here is the table of values I was trying to construct a pattern from:

Since some of these values were multiples of each other I thought something related to time signature was going on. Furthermore a subroutine which retrieves channel/note data gets the index into this table ready.


Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 4 posts ] 

All times are UTC - 7 hours

Who is online

Users browsing this forum: No registered users and 7 guests

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group