Old 29th December 2004, 00:04   #1
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How to reduce Kbps without lowering Khz? -- .MP3 format


I've done a bit of searching on the forums here and haven't found exactly what I'm looking for. I'll start with a description of my current situation and then finish with the specific question.

I've installed a plugin for Winamp to allow it to play .SPC files. These are audio-only files extracted from SNES video games. The audio sounds basically like MIDI but the format keeps all sounds standardized so different hardware/software MIDI implementations don't have any inconsistancies in the sound output (I'm not sure if it actually uses MIDI at all or not).
I've just purchased a portable .MP3 player and want to convert the files from .SPC format into .MP3 so I can play them on the go (yes, I know it's sad that I want to listen to Mario in my car ).
The original .SPC files play in Winamp listed as 16 Kbps and 48 Khz. I've tried copying them at some different Kbps/Khz combinations, and I can hear a loss of quality when I go under 41Khz, so I'd like to keep the Khz at 48. The problem is since the original files are 16 Kbps, there is no reason for me to use anything higher (waste of space), but in the plugin I'm using the lowest Kbps rate I can set with 48 Khz is 96 Kbps. So as of now I've copied numerous .SPC files to .MP3 format at 96 Kbps with 48 Khz. They sound fine, but I've increased the size of the files by almost 10 times in some cases. I'm using the MP3 Output Plug-in by Justin Frankel (http://www.winamp.com/plugins/details.php?id=177) for converting to .MP3 format.
I have tried two other MP3 output plugins, but was not pleased with either one for my purposes.
I figure there will be some size increase from .SPC to .MP3 in general, but I want to keep it as small as possible to maximize the space I have in my player.

At this point, what I need to do is take my current set of .MP3 files--which are at 96 Kbps and 48 Khz--and reduce only the bitrate--from 96 to 16--while retaining the Khz of 48. So bascially I want the files to be 16 Kbps at 48 Khz (as the original .SPCs were) while in .Mp3 format. Is it possible to do this, and if so how do I do it?

Thanks in advance.

Oh, forgot to mention I'm running the latest version of Winamp Pro (yes, I support!), Windows XP, and have the latest version of the Fraunhofer (sp?) Radium .MP3 Codec installed. I'm not sure if any of that is useful information but I figured I would post it just in case.

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Old 29th December 2004, 01:16   #2
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You'll have to use a much higher bitrate than 16kbps.

If the files are like MIDI or SID files they contain mostly information about pitch and duration of sounds (one note in midi takes 16 bytes, one second of uncompressed 16bit/48kHz stereo audio takes 192000 bytes).

16kbps/44kHz isn't possible in mp3 and even if it was its quality would be unbearable.

The lowest possible bitrate at 32kHz or higher is 32kbps, and even it sounds pretty crap, especially when transcoded from 96kbps mp3s.

But if you want to try use the File Writer plug-in with the latest stable lame.exe (or another Lame frontend that allows entering command lines) and a command line like
-b 32 --lowpass 16000, play with the lowpass value to find the one that gives the least horrible result.
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Old 29th December 2004, 03:46   #3
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Well since the original .SPC files were listed as 16 Kbps at 48 Khz when playing in Winamp, would that mean the reading was inaccurate, or is that just something that only that format can achieve? Like I said this isn't actually MIDI, it just sounds similar since it is SNES music. I know they are entirely different formats, and a comparison won't mean too much, but just for an example, the original .SPC file for one song (listed at 16 Kbps and 48 Khz in Winamp) is 64.5 KB, while the same song as a .MP3 (96 Kbps and 48 Khz) is 2.08 MB.

I suppose if the reading for playing the .SPC files is inaccurate, then there is something to this, however if it is accurate that the original files are 16 Kbps, then the increase to 96 Kbps is not going to make the quality any better. I don't know a low about .MP3 format other than it is a lossy format. So I presume taking a 96 Kbps .MP3 down to 16 Kbps would result in data loss, but if the original .SPC file (16 Kbps) were somehow converted to .MP3 at 16 Kbps, the quality should remain the same, shouldn't it?

Basically just trying to figure the best way for me to convert the files to a playable format in my .MP3 player (it only supports .MP3 and .WMA) while saving as much space as possible.


Re-reading your post, I think I may understand better what you meant. The small file size of the .SPC file is probably derived from it having only compressed instructions on pitch and length, while .MP3 is true audio, therefore requiring more bytes per second for the same note, and thus larger filesize. Is that correct, or am I still misunderstanding?

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Old 29th December 2004, 05:11   #4
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Was reading this thread and got curious about it. My initial thoughts were that SPC files must be like MOD files in that they contain digitized Instrument Samples and then notation data to go along with it. I found the following which confirmed my hunch.
Super NES music dumped from the original game ROM using an emulator such as ZSNES and named after the SPC chip in this system. Its method was similar to MOD in that it contains samples and notation data, but in the SNES this was all stored in 64KB RAM. As such the files are always 64KB in size. The SNES had a very unique sound and games like F-Zero and Starfox just don't sound the same any other way
This explains their smaller size.
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