cobra2
All load/save operations to/from the SD Card in the WK-7500 (with the exception of AUDIO files) are made to/from the MUSICDAT folder on the card. You can create this folder manually in a computer, or allow the WK-7500 to create it automatically by formatting the card in the WK-7500. If you ever intend to record audio files with the WK-7500, it is best to format the card in the keyboard to ensure proper formatting that is compatible with Casio audio files.
Load/save operations to/from the SD Card are covered on Pages 138 and 139 of the User's Guide. The "key" is in Step 4 on Page 138. You must press AND HOLD the FUNCTION button while momentarily pressing the (F+) LOAD/SAVE button. This button also serves as the CARD button. This puts the WK-7500 into the LOAD/SAVE mode. BUT . . . prior to doing this, you must first perform one of the operations listed in the table in Step 3 on Page 138 in order to tell the WK-7500 what you want to LOAD/SAVE. If you want to save a User Rhythm to the SD Card, you must first press the USER RHYTHMS button to put the keyboard into that mode before entering the LOAD/SAVE mode, and so forth and so on.
When you record a song with the Song Sequencer, it is automatically saved to internal memory (up to 5 songs), when you press the STOP button to end recording. No additional "save" operation need be done at this point. If you want to save that song to the SD Card, you must press the SONG SEQUENCER button to put the WK-7500 into the Song Sequencer mode (if it is not already there) per Step 3 on Page 138. Use the Data Wheel or the -/+ buttons to select the song from internal memory that you want to save to the card. Now perform Step 4 on Page 138 to enter the Load/Save mode. The display will show "-Seq Load-" and the name of the first file that can be loaded from the card or "No File" if there are none there yet. If you did want to load a sequencer file, you could use the Data Wheel or the -/+ buttons to scroll through the available files, but for now, press the DOWN ARROW button once, and the display will show "-Seq Save-". This is to save the song to the card in Casio proprietary "CMS" format. Press the DOWN ARROW once again, and the display will show "-Seq SmfSave-" This is the one you are looking for. This converts the song to Standard MIDI File Format and saves it to the card as a ".MID" file. This is a 3 item menu. As you continually press the UP/DOWN ARROWS, you just keep looping through these same 3 Load/Save options. Use the Data Wheel or -/+ buttons to name your file (song) and press enter. If you save the song in Seq (CMS) format, you would use these same procedures to load the song back into internal memory to play it, but once it is converted and saved as an SMF (.MID) file, you just press the CARD button from the main power-on screen, and use the Data Wheel or -/+ buttons to select the song to play and press the START/STOP button in the RHYTHM/SONG CONTROLLER transport controls. SMF (MID) files are played directly from the card. They are not loaded back into internal memory to be played. As a matter of fact, you can use a computer to copy SMF (.MID) files into the MUSICDAT folder on the card and play them with the WK-7500's MIDI file player.
Making data backups to the SD Card is covered in the right hand column on Page 139 of the User's Guide.
I realize that all of this is a little more involved than on the older Casio units, but particularly on the CTK-7000/WK-7500, things have been complicated by the inclusion of a Pattern Sequencer as well as the Song Sequencer and by their ability to handle audio files. Just give yourself some time to get used to it. As you have probably already discovered, the manual doesn't help all that much. I just wish the manual writers at Casio would learn what an INDEX is, and what it is for, and how handy it makes finding what you are looking for, but in the meantime, that's part of what this forum is here for.
Recording and playing back AUDIO files with the WK-7500 are covered on Pages 121-126 of the User's Guide. AUDIO files are recorded directly to the SD Card, NOT to internal memory. They are stored in a hidden partition on the card, so Windows and MAC/OS will not be able to see them on the card. That is why you need to format the card in the WK-7500 if you want to record AUDIO files. To convert them to "standard" audio formats, you need to upload them to a computer with Casio's Data Manager 6.X software. If you have problems with this, give a shout once you get into it.
Good luck !
P.S. - Love the car !