1992 Layout Page

2006 Layout Page

2009 Layout Page

P&LE Postcards by Howard Fogg 

Plasticville Buildings

Portable Layout Page

Train Clubs

Bing Track

Remote Train Control Program

YouTube Channel

OOK Radio Support

Technical Videos

3D Prints for my Layout

More RTC Videos

P&LE McKees Rocks Locomotive Shop
3D Printer Project

White Tower Restaurant
3D Printer Project

RFID Train Detection

Frames are 16bit (65,536 byte frame size).
Audio is referenced as Frame number + offset in sample count.
Audio samples are 4bit ADPCM (i.e. 512 bytes = 1024 samples).
All calculated offsets for audio records are in reference to the beginning of the audio data which is at 0x8000 in the .mth file.

//1st audio record
0x0100: 01 // Frame (Start)
0x0101: 00 00 // Offset sample count into frame for start of audio data (16bit big endian)
0x0103: FF FF FF // majority of records defined this way. when not, references a frame + offset as above. unknown, maybe loop data
0x0106: FF FF FF // majority of records defined this way. when not, references a frame + offset as above. unknown, maybe loop data
0x0109: 00 00 00 // majority of records defined this way. when not, pattern is apperent but haven't analyzed it yet.
0x010C: 01 // Frame (End)
0x010D: CE 79 // Offset sample count into frame for end of audio data (16bit big endian)
0x010F: 0B // not known yet. seems to be a bitmask or referenced in nybbles. probably sample rate and other flags.
//result: start @ 0; end @ 52875; 52875 samples

//2nd audio record
0x0110: 01
0x0111: CE 7A
0x0113: FF FF FF 
0x0116: FF FF FF 
0x0119: 00 00 00 
0x011C: 02 // second frame, so add 65,536 to offset
0x011D: F4 6B
0x011F: 0B
//result: start @ 52876; end @ 128107; 75231 samples

//3rd audio record
0x0120: 02
0x0121: F4 6C
0x0123: FF FF FF
0x0126: FF FF FF
0x0129: 00 00 00
0x012C: 03 // 3rd frame, so start at 65,536*2 this time (frame_size*(n-1))
0x012D: D5 03
0x012F: 0B
//result: start @ 128108; end @ 185603; 57495 samples

@echo off

if "%~1"=="" (goto error)
Set filename="%~1"
echo.Filename is: %filename%

Set Folder="%~dp1"
echo.Folder is: %Folder%
Set Name="%~nx1"
echo.Name is: %Name%

rem Check that the extension is .vox
set Ext="%Name:~-4,-1%"
rem echo %Ext%
if not %Ext%=="vox" (goto exterror)

rem Strip the extension and replace it for Outname
set Outname="%Name:~1,-5%.ima"
echo.Outname is: %Outname%

set SampleRate="none"
If NOT %Name%==%Name:5512=% (set SampleRate="-r 5512")
If NOT %Name%==%Name:11025=% (set SampleRate="-r 11025")
If NOT %Name%==%Name:22050=% (set SampleRate="-r 22050")
if %SampleRate%=="none" (goto samperror)
echo.SampleRate is: %SampleRate:~1,-1%

rem echo.Current Folder is:
rem
cd /d %Folder%
rem
pause

echo "C:\Program Files (x86)\sox-14-4-2\sox" %SampleRate:~1,-1% %Name% -e ima-adpcm -c 1 %Outname%
"C:\Program Files (x86)\sox-14-4-2\sox" %SampleRate:~1,-1% %Name% -e ima-adpcm -c 1 %Outname%
rem
echo Import this file into a sound file using ADPCM as a 4 bit ADPCM clip
rem
pause
goto end
:samperror
Echo You must have the sample rate as part of the filename
pause
goto end
:exterror
Echo You can only use *.vox files
pause
goto end
:error
Echo You did not enter the input file name.
pause
:end

So happy to have found this thread - and really appreciate the work done to decipher the MTH sound files and assemble a program to manipulate the sounds inside.

I have a PS2 steamer pulling my Polar Express around our Christmas village.  Not only were the sounds not really appropriate for the Polar Express, but the command environment made it so the conductor announcement car was not functional.  This is no longer an issue!

Following the directions above, I was able to use ADPCM, Audacity, and sox to successfully replace all of the engine sounds this afternoon.  The only caveat, I was never able to export from Audacity to vox format for sox conversion.  Instead, when exporting from Audacity, I set "Save as type" to "(external program)".  The command was specified as

"C:\Program Files (x86)\sox-14-4-2\sox.exe" -t wav - -e ima-adpcm -c 1 "%f"

allowing Audacity to pipe its wav output directly into sox, skipping the intermediate vox step.

Thanks again!
-Sam

@echo off
rem Updated 1 Mar 2018
if "%~1"=="" (goto error)
Set filename="%~1"
echo.Filename is: %filename%

Set Folder="%~dp1"
echo.Folder is: %Folder%
Set Name="%~nx1"
echo.Name is: %Name%

rem Check that the extension is .raw
set Ext="%Name:~-4,-1%"
echo %Ext%
if not %Ext%=="raw" (goto exterror)

rem Strip the extension and replace it for Outname
set Outname="%Name:~1,-5%_be.raw"
echo.Outname is: %Outname%

set SampleRate="none"
If NOT %Name%==%Name:5512=% (set SampleRate="-r 5512")
If NOT %Name%==%Name:11025=% (set SampleRate="-r 11025")
If NOT %Name%==%Name:22050=% (set SampleRate="-r 22050")
if %SampleRate%=="none" (goto samperror)
echo.SampleRate is: %SampleRate:~1,-1%

rem echo.Current Folder is:
rem
cd /d %Folder%
rem
pause

echo "C:\Program Files (x86)\sox-14-4-2\sox" -t .s24 -c 1 %SampleRate:~1,-1% -B %Name% -c 1 %Outname%
"C:\Program Files (x86)\sox-14-4-2\sox" -t .s24 -c 1 %SampleRate:~1,-1% -B %Name% -c 1 %Outname%
rem
echo Import this file into a sound file using ADPCM as a 24 bit signed big-endian clip
rem
pause
goto end
rem
:samperror
Echo You must have the sample rate as part of the filename
pause
goto end
:exterror
Echo You can only use *.raw files
pause
goto end
:error
Echo You did not enter the input file name.
pause
:end

@echo off

if "%~1"=="" (goto error)
Set filename="%~1"
echo.Filename is: %filename%

Set Folder="%~dp1"
echo.Folder is: %Folder%
Set Name="%~nx1"
echo.Name is: %Name%

rem Check that the extension is .ima
set Ext="%Name:~-4,-1%"
echo %Ext%
if not %Ext%=="ima" (goto exterror)

rem Strip the extension and replace it for Outname
set Outname="%Name:~1,-5%.vox"

echo.Outname is: %Outname%
rem echo.Current Folder is:
rem
cd /d %Folder%
rem

echo "C:\Program Files (x86)\sox-14-4-2\sox" %Name% -e oki-adpcm -c 1 %Outname%
"C:\Program Files (x86)\sox-14-4-2\sox" %Name% -e oki-adpcm -c 1 %Outname%
rem
echo Import this file into Audacity as VOX-ADPCM
echo Select Import -- Raw Data
echo Pick the .vox file created by this batch file
echo Select Encoding: VOX-ADPCM
echo Select Byte order: Big-Endian
echo Select Channels: 1
echo Select Sample rate: 5512.5/11025/22050 as necessary
echo Press [Import]
rem
pause
goto end
rem
:exterror
Echo You can only use *.ima files
pause
goto end
:error
Echo You did not enter the input file name.
pause
:end

• WD - The wheel diameter in mm
• GR - The gear ratio (typically 10.50 for diesels and 18.00 for steam engines - but might be different)
• NS - The number of stripes on the tach wheel (typically 24 - but might be different)

It uses these fixed parameters:

• 5280 feet/mile
• 12 inches/foot
• 48 (O Scale)
• 25.4 mm/inch
• M_PI = 3.14159265358979323846264338327950288
• "Smile" is a scale mile - 110 feet in O Scale - or 110 feet/Smile.

Here is my code directly from my C program:   

    K = (12 * 5280/48);    // 1320 inches/Smile
    // multiplier of 2 in the next equation seems to be because both the
    // leading edge and the trailing edge of each stripe generates a count
    TS = 2 * ((K)/((WD / 25.4) * M_PI)) * NS * GR;

    // The meaning of the divisor of 11 in the next equation is DTOFACTOR. Test runs over
    // measured distance show that it is exactly needed to generate
    // correct distance reporting by the engine. Three ways to write the final equation:
    SF = TS / 11;
    SF = TS / DTOFACTOR;
    SF = TS / 110 / 10; 
    SF = TS * 10 / 110;

This SF value is converted to hexadecimal and loaded into RAM at addresses 0x08 and 0x09 (big endian).

• WD - The wheel diameter in mm
• GR - The gear ratio (typically 10.50 for diesels and 18.00 for steam engines - but might be different)
• NS - The number of stripes on the tach wheel (typically 24 - but might be different)

It uses these fixed parameters:

• 5280 feet/mile
• 12 inches/foot
• 48 (O Scale)
• 25.4 mm/inch
• M_PI = 3.14159265358979323846264338327950288
• "Smile" is a scale mile - 110 feet in O Scale.

    K = (12 * 5280/48);    // 1320 inches/Smile
    // multiplier of 2 in the next equation seems to be because both the
    // leading edge and the trailing edge of each stripe generates a count
    TS = 2 * (K/((WD / 25.4) * M_PI)) * NS * GR;
    // the meaning of the divisor of 11 in the next equation is not known. Test runs over
    // measured distance show that it is exactly needed to generate
    // correct distance reporting by the engine.
    // Calculate Scale Factor
    SF = TS / 11;
    //
    // Calculate Speed Factor
    // Constant was calculated by Gear Ratio Spreadsheet (if anyone wants this, let me know)
    // 31.9288 ms/tick_of_DCH
    SpdF = (4973087 * 31.9288) / (SF * 11);

This SpdF value is converted to hexadecimal and loaded into RAM at addresses 0x04 and 0x05 (big endian). My equations match the value in the sound file to within 0.05 percent.

• WD - The wheel diameter in mm
• GR - The gear ratio (typically 10.50 for diesels and 18.00 for steam engines - but might be different)
• NS - The number of stripes on the tach wheel (typically 24 - but might be different)

It uses these fixed parameters:

• 5280 feet/mile
• 12 inches/foot
• 48 (O Scale)
• 25.4 mm/inch
• M_PI = 3.14159265358979323846264338327950288
• "Smile" is a scale mile - 110 feet in O Scale.

    // Number of stripes for one rev of driving wheel * 2 = Number of DTO counts for one rev of driving wheel
    // Number of stripes for one rev of driving wheel = gear_ratio * number of stripes on tach strip
    // Divided by 4 to set 4 chuffs/revolution (use divisor depending on how many chuffs/rev you want)
    CF = NS * GR * 2 / 4;

This CF value is converted to hexadecimal and loaded into RAM at addresses 0x18 and 0x19 (big endian).