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Author Topic: [MegaDrive] Ladder Effect / Distorted sound  (Read 1122 times)

Offline AceMan

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[MegaDrive] Ladder Effect / Distorted sound
« on: October 07, 2017, 08:17:58 PM »
Hello there.
I don't know if it's a bug with the tracker, player or my console, so sorry if it's the wrong section.

I have a problem with FM instruments in MegaDrive modules (every single one of them).
I attached the very basic example module together with recording from my MegaDrive. Please take a look at them and compare.

There is that strange background tone, that doesn't want to fade out no matter what I do.

I am using:
- Deflemask v0.12.0 on Windows
- Deflemask rom export
- SEGA MegaDrive PAL (the very first model with "High Definition Graphics / Stereo Sound" letters on the case)
- Mega Everdrive X3 with latest firmware

Any ideas what could be wrong? :(
« Last Edit: October 08, 2017, 08:54:46 AM by AceMan »

Offline marcb0t

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[MegaDrive] Problem with FM instruments fade out
« Reply #1 on: October 07, 2017, 10:04:46 PM »
Greetings AceMan,

1. Well, the first problem is that the "TL" values are awfully high for the first 2 operators. I lowered them down a bit, and tried to make your instrument keep it's intended sound.

When using Algorithm 7, you are essentially doing additive synthesis with 4 sine waves. They have a tendency to amplify each other with each additional layering with double intensity... with each tone. So your output starts to clip because it is too loud. Try keeping Algo 7 instruments under 12 TL for all the operators, and change the "DT" values a little to decrease the compounding effect of straight tone amplification.

I attached a modified version of your example module.


2. I hear something called the "laddering effect" which was common on the model 1 systems. It is a part of one of the messed up registers on the original ym2612 sound chip. Essentially, there is an interference with some of the delayed instrument sound being regurgitated by the DAC controller. On a Mega Drive with good analog DAC circuitry, it is not very noticeable. But on some MegaDrives (even a few High Definition units) Sega decided to use cheap alternatives for the circuitry. This can sometimes cause some nasty, dirty distortion like you're hearing.

So, just try out the modified module I attached.

If you are concerned about it being too quiet now... All you do is simply lower the volume of all your other channels by 3 or 4 notches to balance everything out. This will also help in reducing clipping and distortion from hitting the top of the decibel wall.

FM instrument designing is often about balance with "TL" values, and how it interacts with other instruments in your track.

Hope it works out!   :)

Offline marcb0t

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[MegaDrive] Problem with FM instruments fade out
« Reply #2 on: October 07, 2017, 10:11:41 PM »
And just so you're aware, I guarantee you that background tone you hear is simply because of the MegaDrive itself. It could last throughout the whole song.

But when you have all the other instruments playing during your song together, it will hardly be noticeable.

It becomes especially noticeable when you have only one or 2 sounds playing with no other accompaniment at high volume levels.

Offline AceMan

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[MegaDrive] Problem with FM instruments fade out
« Reply #3 on: October 08, 2017, 08:54:05 AM »
Thank you for detailed explanation!

After reading a bit further into the topic, it seems that the "ladder effect" is the main cause.
It's mostly unavoidable, so instead of making the sounds quiter, I think I will have make them louder instead to cover the additional hum.
And cut off / fade out quickly. Too bad I really enjoy ambientish, long lasting sounds :D

Ps. I changed the topic title to make it easier to find by potential readers with same questions.

Offline marcb0t

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[MegaDrive] Ladder Effect / Distorted sound
« Reply #4 on: October 09, 2017, 01:37:35 AM »
Thank you for detailed explanation!

After reading a bit further into the topic, it seems that the "ladder effect" is the main cause.

Well, "ladder effect" is simply the root cause.

But what I'm hearing in your recording goes far beyond just the laddering effect.

There is a lot of nasty analog distortion which is making it much worse.

But I cannot tell if it's because of cheap analog DAC hardware, or if it's a wire connected to your speaker, or what else.

Hmmm... It could be since the system is so old, that some of the capacitors need to be replaced, and are not working at their fullest ability anymore. It's common for older gaming sound equipment to require that.

Hey, I like ambientish long lasting sounds as well!

If I send you one of my more ambient deflemask modules through a personal message, would you be willing to send me a wav recording from your Mega Drive?

I'll match the tempo in PAL as close as I can.

Basically, I'd like to hear how the distortion sounds with a more full song like that...
And honestly, I would really enjoy hearing this song on real hardware for once... hehe! Perhaps you might like it as well.

Offline AceMan

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[MegaDrive] Ladder Effect / Distorted sound
« Reply #5 on: October 09, 2017, 05:44:46 AM »

There is a lot of nasty analog distortion which is making it much worse.

But I cannot tell if it's because of cheap analog DAC hardware, or if it's a wire connected to your speaker, or what else.

Hmmm... It could be since the system is so old, that some of the capacitors need to be replaced, and are not working at their fullest ability anymore. It's common for older gaming sound equipment to require that.

Well, you may be right. I don't have any other system to compare.
But we have a retro event in 2 weeks ( http://retrokomp.org ) so I will be able to test the sound on various MDs I hope.

Quote
If I send you one of my more ambient deflemask modules through a personal message, would you be willing to send me a wav recording from your Mega Drive?

I'll match the tempo in PAL as close as I can.

Basically, I'd like to hear how the distortion sounds with a more full song like that...
And honestly, I would really enjoy hearing this song on real hardware for once... hehe! Perhaps you might like it as well.

Of course! I can make the recording everyday in the evening.