ZOOM H4n Material lost on SD Card

[Karl Chelette]

Hi all, I’ve just cracked the 4 and 8 track corrupt audio file problem, which is a 3 second echo of each track after importing raw into Audacity. This happened from sound guy turning powerstrip off with no batteries in unit. Here are the steps I used: First I made image file of the sd card with the lost files, then I took an old sd card and wrote all zeros to it, formatted it. Then made a short test recording with the same format, saved it and turned it off properly.
Then I made an image file of the test recording and opened it up in HXD hex editor. I found out that with my zoom r24 recorder, when recording, it records 393216 bytes of each channel sequentially and when done writes the wav header with data location, recording format etc. When turned off improperly the wav header is not written and the data that is there is in alternating blocks of each channel.
Using HXD hex editor I found the start of the data and saved this as a new file, which I then used the split option in HXD and split the file into chunks of 393216 bytes, named 0001 and up. Then I opened the folder with the file chunks into it and squised the screen down till I could view 2 rows of files, about 4,000 of them. Then I selected the odd row on the left and cut and pasted it into a new folder. Then using HXD, I concatenated (joined) the odd file numbers together, then did the same for the even ones. This left me with in my case, the data for both mono channels. Then I imported the test recording file in HXD and pasted the recovered data into the proper space, which was at 60000 hex location. The next thing I had to alter was the last 4 bytes before the data which tell the file length data. Repeated the same for the other channel then voila, both channels recovered, no echo, synced properly, 3 hours worth back!!!!!

[Chris Hunziker]

Thanks Karl for this detailed report. It sounds very complicated – and I don’t know, if I could manage to do all this without messing up.
That’s why I think Zoom should write a small software that automates all these steps. Or is anybody out there who could do that? I am sure the demand is there, but I am not able to it myself, sorry.

[Karl Chelette]

Chris, I don’t think it’s possible to automate this process because the start and end of the data chunk must be determined and this info is lost when the unit loses power. On any given chip there might be half a dozen data chunks floating around from long ago deleted recordings. If you can make a disk image of your sd card and make a disk image of a sample recording in the same format, since I don’t know the data chunk size of the H4n, put them on a usb drive and send it to me, I’ll recover it for you, put it on your usb drive and mail it back to you and call it a merry christmas to you! P.O. Box 2387 Nevada City Ca, 95959

[Chris Hunziker]

Thank you very much for your kind and generous offer, Karl. The fact is, that in the end I had to finish the concert video without the H4n recording. I had to spend some extra time to beef up the audio that was on the closest camcorder, which went ok (as I cannot compare it to the H4n recording, I don’t know how much better that would have been, but the customer wanted to have the product asap.)

So again, thank you very much and Merry Christmas to you.

PS: I was just disappointed by the reaction of the Zoom Company after I contacted them telling me, that they built in a solution for the H2n but not for the H4n.

[Jackson Notier]

Hi Karl,

Thanks a lot for your post, with your solution for the 4/8 channel files!

I lost power on a performance recording about 10 minutes (4CH), than I turned it back on and without knowing to change cards, recorded another 10 minutes. Do you think your solution would work, or did I record over the original recording?

Thanks!

Jackson

[Karl Chelette]

Hi Jackson, what I would do is make an image of the sd card, then import all of it into Audacity as raw, experiment with the start offset, 0-4 until you get something that plays. Then you could search through it to find out if you recorded over it or not. You could then maybe use Audacity to trim off the beginning and resave it. That way when you go looking for the start of data in the hex editor you won’t have to sift through so much data. In order to recover, you have to find the exact start off data and know the data chunk size, so you can manually un-interleave it. In my case there was a whole lot of 0’s before the data started. Let me know what you find. I’m just now starting to work on a set of lost files from a Sony DR680 and I don’t think it is going to be as easy as the Zoom.
Karl

[Ben Doyle]

Hi Karl,

I’ve got a “lost” Zoom (in my case the R16) 5 channel multitrack file that was recording a concert and was unplugged accidentally by one of the musicians. I’m able to recover a wav file using the import of raw data feature in both Audacity and Adobe Audition, but the file is interleaved since I recorded 5 channels. It sounds fine except for that. I’ve tried your suggestion of opening in a hex editor after comparing the data to a properly recorded 5 channel file, but this is super complex for me. Anyway, I’ve got a frantic client who is needing to know if recovery of this audio is even possible. Can you help? I’d be happy to pay you.

[Karl Chelette]

Hi Ben, Sure, I can help. I would say recovery is almost certainly possible unless you recorded something else on the sd card. You will need to get me a disk image of the sd card. My dropbox is only about 5 gigs so anything bigger you’ll have to mail to me, unless you have a bigger dropbox or cloud storage. Get it to me and I’ll start working on it right away. When I’m done I’ll be able to upload them to my dropbox for you. How long are the tracks you are trying to recover?

[Ben Doyle]

Thank you so much Karl! So it’s about 90 minutes of concert straight through, and I recorded it to 5 mono tracks on the R16. It was 3 amps and a stereo mic pair of overhead cardioids. I recorded to a 32 GB Transcend SD card and didn’t record anything else on it afterwards. Like I mentioned, when importing the raw data I can hear the entire concert, but with the interleave multitrack issue of course. I created an image of the card (DMG on mac) once I got it back to my office. So is there a way to provide you a smaller file instead of the full sd card image? Can I save the raw audio data out of Adobe Audition maybe as a smaller file so you don’t have to get the whole 32GB DMG image? Additionally, I recorded a 5 channel (same exact setup) test clip which was 30 seconds to have as a proper reference. Do you need that 32GB image as well or is there a way to provide you with that reference track smaller also? Feel free to contact me offline at ben@runawaypro.com. Thanks again!

[Adam Bankhead]

WOW Karl. I knew it was possible. Thank you for figuring this out. I’m several hours into whatever hex editing online tutorials I can find, and my mind is still blown trying to figure this out. I zeroed out another SD card, did a test recording with the same settings, and I don’t even know where to begin. I THINK I can guess where the audio information starts, and maybe where the header info is, but I’m just guessing. The fact that the rest of the data are zeroes makes it slightly easier, but I still have NO IDEA how to interpret this data. And forget about interpreting the data on the original SD card that is surrounded by data from previous recordings, etc.

Furthermore, I don’t know HOW you determined how many bytes of each channel your recorder writes sequentially, or how you managed to further split the data into the mono channels, or how you found the data on the original card where the header was written improperly or not at all… I don’t know how you did any of this. 5 hours into hex tutorials, I’m still drowning in a sea of gibberish characters. You are a crazy mad hacker genius.

I’d love to be able to do this myself, but this might be more of a time investment than I can afford. Can I pay you to do this recovery for me?