This is a summary of information contained in Microsoft's
Knowledge Base article ID: Q141801 

Troubleshooting Audio CODECS in Windows 95

Missing CODECS 

Windows 95 includes 32-bit versions of several common CODECS. These 
32-bit CODECS are installed by default during Windows 95 Setup when 
a sound card is installed in the computer, and are used by multimedia 
programs even if a 16-bit version of the same codec is available. 

To verify that the 32-bit CODECS included with Windows 95 are 
installed, follow these steps: 

 1. In Control Panel, double-click Add/Remove Programs. 
 2. Click the Windows Setup tab. 
 3. Click Multimedia, and then click Details. 
 4. Verify that the Audio Compression check box is selected. If it 
    is not selected, click the check box to select it, and then click 
    OK. 

PhoneFree uses the following 32-bit CODECS included with Windows 95: 

DSP Group Truespeech Software 
Microsoft Groupe Special Mobile (GSM) 6.10 

You can verify that these codecs are installed by following these 
steps: 

 1. In Control Panel, double-click Multimedia. 
 2. Click the Advanced tab. 
 3. Double-click the Audio Compression CODECS branch to expand it. 

If the codec used to compress the file is not listed, install that 
codec using the Add New Hardware tool in Control Panel. To do so, 
follow these steps: 

 1. In Control Panel, double-click Add New Hardware. 
 2. Click Next, click No, and then click Next. 
 3. Click Sound, Video, And Game Controllers, and then click Next. 
 4. To install the GSM 6.10 CODEC, click Microsoft Audio CODECS in the 
    Manufacturers box, and then click the GSM entry in the Models box. 
    To install the DSP Group Truespeech Software codec, click DSP Group 
    in the Manufacturers box, and then click TrueSpeech(TM) Software
    CODEC in the Models box. 
 5. Click Next, and then click Finish. 

Disabled or Damaged CODECS 

If you still cannot play a particular .wav file after verifying that the 
codec used to compress the file is installed, the codec may be disabled 
or damaged. To verify that a particular codec is enabled, follow these 
steps: 

 1. In Control Panel, double-click Multimedia. 
 2. Click the Advanced tab. 
 3. Double-click the Audio Compression CODECS branch to expand it. 
 4. Click the codec used to compress the file that you are attempting 
    to play, and then click Properties. 
 5. Verify that the Use This Audio Codec option is selected. 

To ensure that you are not using a damaged codec, follow these steps to 
reinstall a codec: 

1. In Control Panel, double-click Multimedia.
2. Click the Advanced tab.
3. Double-click the Audio Compression CODECS branch to expand it.
4. Click the codec used to compress the file that you are attempting to
   play, and then click Properties.
5. Click Remove, and then click Yes.
6. Restart your computer.
7. In Control Panel, double-click Add New Hardware.
8. Click Next, click No, and then click Next.
9. Click Sound, Video, And Game Controllers, and then click Next.

Install the codec used to compress the file that you are attempting to
play. To install the GSM 6.10 CODEC, click Microsoft Audio CODECS 
in the Manufacturers  box, and then click the GSM entry in the Models
box. To install the DSP Group Truespeech Software codec, click DSP
Group in the Manufacturers box, and then click TrueSpeech(TM) Software
CODEC in the Models box.

Click Next, and then click Finish.

Conflicts Between 16-Bit and 32-Bit CODECS 

If the 32-bit version of an audio codec that Windows 95 needs to play 
a particular .wav file is not installed or is disabled, Windows 95 uses 
the 16-bit version of the codec if it is available. If the 32-bit version 
of the codec is installed, Windows 95 uses this version by default. However, 
you may experience problems when both the 16-bit and 32-bit versions of a 
particular codec are installed. 

The following 16-bit audio CODECS are installed by the run-time versions of 
Microsoft Video for Windows, Microsoft Windows Sound System, and many other 
Microsoft multimedia programs: 

Microsoft ADPCM 
Microsoft IMA ADPCM 
DSP Group Truespeech Software 

These 16-bit CODECS appear in the [Drivers] section of the System.ini file, 
but do not appear when you double-click the Multimedia icon in Control Panel, 
click the Advanced tab, and then expand the Audio Compression CODECS branch 
of the Multimedia Drivers tree. To disable a 16-bit codec, remark or remove 
the line in the System.ini file that corresponds to that codec. After disabling 
the 16-bit version of the codec, you should reinstall the 32-bit version using 
the steps described in the "Disabled or Damaged CODECS" section above. 

The following lines in the System.ini file correspond to the 16-bit versions of 
the Microsoft ADPCM, Microsoft IMA ADPCM, and DSP Group Truespeech Software CODECS, 
respectively: 

[Drivers]
msacm.msadpcm=msadpcm.acm
msacm.imaadpcm=imaadpcm.acm
msacm.trspch=ts_soft.acm

If you are using a 16-bit program in Windows 95, you may want to disable the 
32-bit version of a particular codec, instead of disabling the 16-bit version. 
To do so, follow these steps: 

 1. In Control Panel, double-click Multimedia. 
 2. Click the Advanced tab. 
 3. Double-click the Audio Compression CODECS branch to expand it. 
 4. Click the codec you want to disable, and then click Properties. 
 5. Click the Do Not Use This Audio Codec option to select it. 
 6. Click OK.