RMT Challenges / Frustration - HELP!

[rdefabri]

I'm working on a new song that will require a prominent, deep bass sound.  Not using joined channels / PWM, just a 15KHz square bass will work fine.  The goal is to create the song in mono / 4-channels.

 

The problem I am running into is when I create an instrument using 15KHz mode.  No matter what channel I have that instrument playing on, it affects the sound of the instruments on any other channel.  In this case, it's affecting the drum track, so much so that it's barely recognizable as drums.

 

Would this happen on a physical A8 or is this something that is related to POKEY emulation in RMT?  It's frustrating because no matter what I try, I can't get it right, and I've shelved the project for now.

 

Any advice or assistance is greatly appreciated!

[Rybags]

It's a limitation of Pokey.

 

The base frequencies and voice combinations have limitations.

If doing 4 voices x 8 bit AUDF then you can usually only have:

All voices 64 KHz based (usual default) or all voices 15 KHz based.

Then you have the option of using 1.79 MHz base on voices 1 and 3 - in this case it will override the 15 or 64 KHz setting for those voices.

Then you have the option of joining voices 1+2 and/or 3+4 - in which case the base frequency of voices 1&3 is used and the combined 16 bit AUDF becomes the frequency value (generally you'd do this in 1.79 MHz mode but doing it in 15 or 64 is also valid though less useful)

 

Assuming you're using just single Pokey and you want those lower frequency sounds then your options would be:

Use 15 KHz on 2 voices then join the other 2 in 16 bit mode.

Use 64 KHz on 2 voices then join the other 2 in 16 bit mode.

(I'm assuming here that RMT should support these options, I'm not an expert on that program)

 

For most needs you'd probably do better using the second option there - the 15 KHz mode has it's merits but for general music the note precision isn't very good.

 

 

Edited November 28, 2023 by Rybags

[rdefabri]

1 hour ago, Rybags said:

It's a limitation of Pokey.

 

The base frequencies and voice combinations have limitations.

If doing 4 voices x 8 bit AUDF then you can usually only have:

All voices 64 KHz based (usual default) or all voices 15 KHz based.

Then you have the option of using 1.79 MHz base on voices 1 and 3 - in this case it will override the 15 or 64 KHz setting for those voices.

Then you have the option of joining voices 1+2 and/or 3+4 - in which case the base frequency of voices 1&3 is used and the combined 16 bit AUDF becomes the frequency value (generally you'd do this in 1.79 MHz mode but doing it in 15 or 64 is also valid though less useful)

 

Assuming you're using just single Pokey and you want those lower frequency sounds then your options would be:

Use 15 KHz on 2 voices then join the other 2 in 16 bit mode.

Use 64 KHz on 2 voices then join the other 2 in 16 bit mode.

(I'm assuming here that RMT should support these options, I'm not an expert on that program)

 

For most needs you'd probably do better using the second option there - the 15 KHz mode has it's merits but for general music the note precision isn't very good.

 

 

Thanks - this really helps!  I didn't realize the limitation was with POKEY.  I guess the other option would be to do stereo and limit 15Khz channels to one side.  Not elegant, but could work.

[makary]

On 11/28/2023 at 4:08 PM, rdefabri said:

Thanks - this really helps!  I didn't realize the limitation was with POKEY.  I guess the other option would be to do stereo and limit 15Khz channels to one side.  Not elegant, but could work.

Yes. Using 15 kHz gives reasonable bass sounds but melodic lines are not very good then. High sounds when using A distortion go quickly out of tune in 15kHz. Some workaround for getting high sounds is using 1.79 mode. I was struggling with that creating this cover and I couldn't get anything better:

 

 

neonlicht.xex

[woj]

I am going through the exact same education pains constructing the soundtrack for Popeye. Having per channel 15k/64k selection would be sooo sweet 😕

[+MrFish]

15 hours ago, makary said:

neonlicht.xex 3.76 kB · 4 downloads

It's pretty-nicely constructed.

 

But you're using some different bass notes than the original. Is this by artistic choice?

 

Part 1 of the song

original: D to higher G

your conversion: D to lower C

 

Part 2 of the song

original: lower A (holds throughout)

your conversion: lower G to lower A

 

I'm not saying it doesn't sound good or anything like that; but it does change the character of the original song in those places.

 

[makary]

5 hours ago, MrFish said:

It's pretty-nicely constructed.

 

But you're using some different bass notes than the original. Is this by artistic choice?

 

Part 1 of the song

original: D to higher G

your conversion: D to lower C

 

Part 2 of the song

original: lower A (holds throughout)

your conversion: lower G to lower A

 

I'm not saying it doesn't sound good or anything like that; but it does change the character of the original song in those places.

 

Thanks for that! I've refered to some midi file of the song. I've rewritten the score into RMT too carelessly I think I'm going to see how it sounds when using the points you made. 

[makary]

10 hours ago, woj said:

I am going through the exact same education pains constructing the soundtrack for Popeye. Having per channel 15k/64k selection would be sooo sweet 😕

Yes, exactly. I've done some hack of RMT for 15kHz. It uses a bit different tuning. Sometimes it works better than regular RMT but still melodic lines are the weakest point in this 15kHz mode.  

Rmt15kHz_v1.exe

[+MrFish]

2 hours ago, makary said:

I've refered to some midi file of the song.

Yeah, some midi and mod authors either take liberties or aren't entirely accurate with their transcriptions.

 

BTW, when I say "lower" or "higher" in my above comparison, I'm speaking in relation to the D bass note used in the main/first part of the song.

 

[Sandor / HARD]

Hi there,

 

That's the reason I made HardBASS. To provide deep bass sound that only affects a single channel and the other 3 can still run in 64KHz mode.

The downside is that you need to be a skilled demo coder to use it - and didn't get integrated into RMT.

 

https://bitbucket.org/sandor-hard/workspace/repositories/

 

Demo song using RMT+HardBASS:

 

[rdefabri]

1 hour ago, Sandor / HARD said:

Hi there,

 

That's the reason I made HardBASS. To provide deep bass sound that only affects a single channel and the other 3 can still run in 64KHz mode.

The downside is that you need to be a skilled demo coder to use it - and didn't get integrated into RMT.

 

https://bitbucket.org/sandor-hard/workspace/repositories/

 

Demo song using RMT+HardBASS:

 

I think this question was answered, but if you use 15KHz mode on a physical A8 computer, can you have the other channels in 64KHz mode?  Or - like in RMT - are all the channels affected?

 

I hope the limitation is RMT, not the A8, but I think this is the case for programming on an actual A8 - is that correct?

[pseudografx]

It's a POKEY limitation.

[rdefabri]

2 hours ago, pseudografx said:

It's a POKEY limitation.

As I suspected - thanks for confirming!