GSM is an audio file format developed as a human speech encoding standard. It was specifically designed to efficiently and accurately process speech based on the fact that human voice does not change more frequently than at 20ms intervals. GSM Codec GSM audio is encoded using GSM codec.
After converting the file to the new format, you will be able to use other programs to support it. Keep in mind, however, that the GSI file after converting to GSM may differ slightly from the original. The most important information should be kept, but if you want the file after conversion from GSI to GSM to be the same, you have to do this carefully and choose the proper application from the list below.
There is no guarantee, of course, that the conversion will come up to all your expectations, but it will certainly help you. If, after all, the effect of converting GSI to GSM does not meet your expectations, you can simply try to find on the Internet a different version of your file in GSI format, properly converted to a GSM file by someone else. If this fails, use the information provided in the further part of the website.
Unfortunately, if after performing the two previously described steps (trying to find your GSI file converted by someone else, and the attempt to convert it to GSM on your own) you still have a problem with your file, then there are only a few solutions left. You can once again try to find and install an application that can open the GSI file in its original format (without conversion to GSM file). Such a solution will be difficult to implement, but it certainly will give the best result.