Some tehcnical questions about YM-2149 composing

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Tolaemon
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Some tehcnical questions about YM-2149 composing

Postby Tolaemon » Mon Dec 29, 2008 11:24 am

I'm a newbie on AtariST's YM-2149 composing, I used to compose songs for the Amstrad CPC's AY-38912 wich is nearly identical, but I would like to know which are the most apreciated effects for AtariSTs composers? I never used the AY's-38912 in built envelope generator in my CPC, do you use it on your AtariST? And I would also like to know about the "SID like" sound that some of you refer in some posts? How can the YM obtain a SID like sound ? Wich are the other interesting efects, a part from sampled sounds or "digidrums" ?

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christos
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Re: Some tehcnical questions about YM-2149 composing

Postby christos » Mon Dec 29, 2008 12:25 pm

I am not even close to being a musician but let's see if I can attempt an answer to your questions. I'd think the most used effects are SID, Digidrums and Buzzer. SID voice is a special interrupt technique that mixes YM sounds with a cpu generated square waveform (if I understand that correctly) in a way that reminds the C64 SID chip but it's distinctly different. Digidrums are as per name, small samples that play on one of the YM channels to add realistic drum effects, while the Buzzer effect is similar to that but makes use of the YM envelope. The biggest difference to what you are used to in the CPC is the fact that you have a very strong cpu on the back to help you with your tune.
Now, if I may suggest, download the SNDH archive found at http://sndh.atari.org/ where you can find most of the tunes ever made on the ST and you could also ask more specific questions at the tracking bbs that most atari musicians visit. http://bbs.dhs.nu/tracking/

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Re: Some tehcnical questions about YM-2149 composing

Postby Tolaemon » Wed Dec 31, 2008 7:03 pm

Thanks for your help Christos. I will take a look to the forums you have posted! And happy new year to evereybody!

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big alec
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Re: Some tehcnical questions about YM-2149 composing

Postby big alec » Tue Jan 13, 2009 8:10 pm

Just from the back of my memory, since I haven't done any YM2149 stuff in almost 15 years:

The envelope generator is used to create bass sounds in a variety of ways. By setting the frequency high in the audible range, the various ramping triangular and saw-tooth waveforms can be used as an alternative to the standard squarewave sound. Also, you can combine the pure envelope-generator sound with the squarewave from the oscillator to create a buzzing effect. Usually you use a frequency ratio that has both generators play either the same note, an octave up or down, or a fifth. To add modulation to the sound you can slightly detune the two oscillators.

The so-called SID effect requires use of a programmable timer interrupt, e.g. like the MFP Timers A,B,C, or D on the Atari ST. Here we use the native squarewave oscillator and additionally program the timer to trigger an interrupt at close to the same frequency of the oscillator. The interrupt service routine then toggles the volume register between zero and the current volume (whatever the volume value in the music player's ADSR envelope). The slight offset between the frequencies causes an effective pulse-width modulation of the square wave, which gives the pleasant movement in the harmonics known as the SID sound.

Tao also invented a technique called Sync-buzzer, which combines the use of interrupt and envelope generator techniques to create some amazing sounds reminiscent of ring-modulation or filtering. But I cannot speak about how that's done exactly, since I have never used it myself.

Hope this helps :wink:

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Tolaemon
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Re: Some tehcnical questions about YM-2149 composing

Postby Tolaemon » Sat Jan 24, 2009 9:29 pm

Thanks for the info, Big Alec. By the way, congratulations for your Propehcy Remake, I've listened it many times!


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