Can a highly compressed DPCM sample be loud? - FamiTracker

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## Can a highly compressed DPCM sample be loud?

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nesrocks
  Posts: 4
  Joined: Sat Aug 20, 2016 3:19 am

### Can a highly compressed DPCM sample be loud?

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Post by nesrocks » Wed Dec 20, 2017 12:20 pm

I'm trying to replace the 4-bit unsigned PCM audio from ghostbusters (NES) with a 1-bit DPCM sample. I have replaced that code the plays it, but there are two things to consider:
1 - I have only $9F0 bytes to fit the sample into.
2 - Whatever I try, the new sample's volume is really low compared to the rest of the game.
This sample is played only on the title screen and nothing else is played along with it (to my knowledge).
Attached is the wave file containing the isolated shout from the song.
Any tips?
I have tried famitracker, RJDMC and tepples' 81.exe. They all give similar results though.

Attachments
  newyell.zip
    (120.33 KiB) Downloaded 196 times

Last edited by nesrocks on Fri Dec 22, 2017 3:40 am, edited 2 times in total.
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PinoBatch
  Posts: 59
  Joined: Fri Oct 13, 2017 11:18 pm

### Re: Can a highly compressed DPCM sample be loud?

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Post by PinoBatch » Wed Dec 20, 2017 2:41 pm

At rate 10 (12604 Hz) the wave is 2401 bytes.
At rate 11 (13983 Hz) the wave is 2657 bytes but is effectively silent after 2513 bytes.
I chose rate 11 for these tests.
The "gain" option in FamiTracker's converter boosts a wave by a given number of decibels before conversion. The drawback of choosing a high gain is that you get slope clipping. When the wave tilts too steeply for the delta modulation to track, the converter tosses high frequencies to keep it in range. I chose +3 dB for these tests.
A custom play routine can increase effective gain. Blades of Steel, among other games, does this to play waves outside the fixed bank. But it does use about 100 bytes.
I've attached the result of rate 11 +3 dB conversion in FT as both a bare .dmc file and as a FTM loop to hear how it'd sound in context.

Attachments
  newyell.dmc
    (2.45 KiB) Downloaded 187 times
  Ghostbusters loop.ftm
    (7.05 KiB) Downloaded 227 times

If MMC5/VRC6 is a crutch, then VRC7 is a wheelchair ♿
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nesrocks
  Posts: 4
  Joined: Sat Aug 20, 2016 3:19 am

### Re: Can a highly compressed DPCM sample be loud?

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Post by nesrocks » Wed Dec 20, 2017 2:50 pm

Thanks for all the info!
Hummm that's very similar to my results. For comparison, the original is at least twice as loud and has no background interference noise, and is 66% smaller. I think I'm going to give up and replace it with 3 square wave notes mimicking the yell...
If you're interested, I have discussed about this here but there wasn't much progress:
http://forums.nesdev.com/viewtopic.php?f=6&t=16823
The original PCM sample is very loud. I noticed the sample in gauntlet 2 is very loud too and doesn't have noise too. Maybe they're the same format? edit: yes it is, just a faster rate, but same format.
edit: I'm going to say this issue has been solved. Check it out here: http://vgmrips.net/forum/viewtopic.php?f=15&t=2892
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