Lost and Found Files

August 30th, 2013 | by Jeff Towne

GlitchCollage

You finished the interview; it was great. You’re ready to transcribe. But… the audio files are missing on your memory card. Or they won’t open. Or they seem to have no data. PANIC! Relax, it may be okay. Jeff Towne tells you what to do. Thank you, Jeff. Jay A

One of the worst experiences you can have during a recording session is this: in the course of an important interview, something goes wrong with your equipment. Sometimes, gear failure can result in a lost interview, but thankfully, some technical disasters have solutions.

Power Sources

One cause of gear trouble: abruptly losing power to your recorder. Perhaps a power cord accidentally disconnected, or batteries fell-out. Maybe a memory card slipped out of its slot while the recording was in-progress. In situations like these, audio data may be written to the memory card or hard drive, but the recorder didn’t have time to save appropriate “header” data. (A file “header” is a small snippet of code saved alongside the audio data, that tells a computer about the contents of the recording.)

batteryEmpty

If the power source is disrupted, most current field recorders will write that header data and properly close a recording before shutting down, but occasionally that function doesn’t work properly. Be sure to use the types of batteries approved for your particular recorder.

Check to see if there’s a menu setting you need to change, based on the chemical formulation of the batteries. Many recorders have a menu setting for Alkaline or Nickel Metal Hydride (NiMH) batteries that allows the display to more accurately predict the battery life. If that is set incorrectly, or if you’re using another kind of rechargeable battery (some recorders don’t like Lithium rechargeable batteries) the remaining charge indicator may not be accurate, and your recorder may shut down abruptly.

Even if you usually record using a cord plugged into AC power, it’s a good idea to have charged batteries in your equipment as well. They can save the day if there’s no convenient outlet, if plugging-in creates a hum or buzz on the recording, or if AC power is interrupted. Many devices will seamlessly switch over to the batteries if AC power is cut.

BatterySelect

Running out of battery life is annoying, but not tragic, because you’ll usually still have useable recordings. If you can swap-in new batteries or use an AC adapter, you can continue where you left off. ALWAYS bring extra batteries. If your recorder uses a proprietary rechargeable battery, have a spare, and make sure it’s charged.

It’s all in your Headers

Occasionally, such sudden power-downs result in sound files with corrupt header information. This is likely to happen if a power cord is disconnected, or the batteries or sound card come out while recording is in progress. Make sure all cables are firmly connected and battery and memory card doors are latched.

Even when taking precautions, sometimes things just go wrong. The result of garbled or missing header information is that most audio software will be unable to play back your file. Your memory card or hard drive will show a sound file with a .wav extension, and the file will have an appropriate size (approximately 5 megabytes per minute for mono, 10 megabytes per minute for stereo, if you recorded at 16 bit and 44.1 khz) but that soundfile will not play back properly, and will not import into most audio editors.

A recent real-world example: I got an urgent email from an experienced Public Radio producer that said …

I just got back from the most amazing interview… but the recorder (Marantz 620) self powered down a bunch of times during the interview. Batteries were fine. Not sure what was causing it. But I just kept my fingers crossed that the files would be ok when I got home. But… seems I’ve lost a bunch of the audio. I can see the files, but they won’t play.

Is there a way to recover them? Please tell me yes.

The files can’t be recognized in pro tools. And they show ‘0’ duration. But they do show size (1.3mg, 94mg etc)
I’m attaching one of them for the hell of it.

Grateful for any suggestions.

BacklineThis showed all the symptoms of corrupted or missing file headers. The recorder had abruptly shut off several times. He could see the files on the memory card, and each file contained some data, as reported by the file size (it’s bad news if the file is 0 bytes, or any very small number of bytes.)

Sure enough, I tried to open one of the files in Pro Tools, but the program did not recognize it as an audio file. I could not play it in iTunes. Attempting to import the files crashed Audacity.

Get your Headers examined

Thankfully, all was not lost. There are a few utilities that can repair corrupted file headers. Audiofile Engineering makes an application for Mac OS called Backline that can diagnose and fix many audio file problems. Its Audio File First Aid can repair missing or damaged headers and many other audio file problems.

AudioFileFirstAid

Opening the file in Audiophile First Aid reported that “the IFF size is smaller than the content of the file,” and offered to increase the IFF value to match the length of the file, or to truncate the audio to match the IFF value. I chose to extend the file, hoping to recover all recorded data. The program indicated that the prognosis for succeeding at extending the audio was worse than truncating, but that would result in a shorter file, and loss of some audio content. Luckily, after a couple of passes, Audio File First Aid did repair the file, and maintained its full length, without truncating.

Backline is not very expensive, but there’s even better news: some of these problems can be fixed with the free audio editor called Audacity. Audacity will run on many operating systems, and is a small and efficient program, so it’s handy to keep around even if it’s not your primary audio editing tool.

Trying to import the corrupt file into Audacity as an audio file crashed the program, but there’s another option: to import as Raw Data. (File>>Import>>Raw Data…) It’s important to know something about the file when importing as Raw Data. You will be presented with an import dialog asking for the sample rate, the number of channels (one for mono, two for stereo, more for interleaved multitrack files), the kind of encoding (in this case, 16-bit PCM). It will also ask for an oddly-named parameter called “Little-Endian” or “Big-Endian.” The disc formats that most current field recorders use, FAT 16 or FAT 32, write WAV files with accompanying metadata at the end, known as “Little Endian.”

AudacityImportRawThere are a few other settings, but it’s usually best to try the defaults first and see what happens. In this case, it worked fine with the default settings, but if the file did not import correctly, it’s worth trying some variations in the start offset value. If the file opened, but was full of static and other noise, try again with the “Start Offset” set to 1 sample. Once the file is successfully imported, you will have to Export it as a standard WAV file in order to re-write the correct header data. Don’t just hit SAVE in Audacity, that will merely save your session information, you must Export to make a new file.

If you happen to use Hindenburg Journalist as an audio editor, you have another tool at your disposal. Hindenburg was able to import these glitched files with no complaints. The files appeared in the Hindenburg session at the correct length and played fine, with no audible artifacts. As with Audacity, you need to Export these files from the session, creating new, clean WAV files with correct header information.

So, if your recorder suddenly shuts down, or someone trips over your power cord, you MAY still be able to recover your recordings up to the point where you lost power.

If you can’t Rebuild, Recover

AudioFileFirstAid2Sadly, rescue is not always that easy, or even possible at all. Occasionally files get corrupted beyond where they’re recoverable with these methods. Sometimes memory cards and hard drives get corrupted to the point where you can’t even see the files. If that happens, it could be that the index of files the operating system writes on each storage device to organize data (the directory), may have become corrupted.

The good news is that often, files can be recovered by using software that will rebuild the directories, returning the card or drive to its original state, or with file-recovery software that can search a corrupted drive and save files to a separate location. For more on what to do when this happens, check out this article on Transom.

But sometimes data loss is more serious: sometimes hardware fails, and when that happens, you may lose recordings permanently. There are companies that will attempt to recover data from dead hard drives, but their services are usually very expensive, and not always successful. So, back-up your recordings as promptly as possible. Save at least two copies of your raw recordings, on separate media (not two folders on the same hard drive) and ideally, store them in two separate physical locations.

Back-up in the field

If you have a recorder such as the Sound Devices 722, take advantage of the fact that it can simultaneously record to both its internal hard drive and a Compact Flash card. If you don’t have a recorder that makes its own back-ups, and your interview is urgent, unrepeatable or irreplaceable, consider running a second recorder as a back-up, just to cover those cases when disaster strikes. Use a mic splitter to send your microphone signal to two recorders, or take a line output from your primary recorder and connect that to the line-in of a back-up recorder (use the headphone output if there isn’t a dedicated line-out). If using the headphone out of the primary recorder as a line-out, be sure to connect headphones and monitor from your back-up recorder.

One of the biggest heartbreakers in the recording experience is accidentally leaving your recorder in pause. It’s also a common mistake, something of a rite of passage. Many recorders automatically go into record-pause mode when pressing the record button, and that’s handy for setting input levels, positioning your mic, and adjusting your headphone level. However, it’s also dangerous: the meters are bouncing and you can hear sound in your headphones, so it’s easy to assume that a recording is in progress.

There’s no universal standard for how the record light looks; some recorders flash a red light when in pause, which changes to a solid red when rolling. Others do the opposite. Make sure you know which protocol your recorder follows, and even more important, make sure to check your display and make sure that the time counter is moving, because there’s no after-the-fact fix for that error – there’s no data to recover!

And as always, use your headphones. Lost or corrupted data can be a big problem, but it’s just as bad to have your recording ruined by a crackling or buzzing short in your mic cable, or by cellphone interference, or because a dead internal battery stops supplying phantom power, or because your mic placement results in severe P-Pops, or any of a myriad of things that can go wrong; problems you can address in the moment, if you’re paying attention.

Now, stop reading articles on the internet and get back to work. Aren’t you supposed to be making back-ups of something?


One Comment on “Lost and Found Files”

  • Flawn Williams says:

    I don’t think “big endian” and”little endian” have anything to do with the data volume formats like FAT16, FAT32, or where the metadata is written. The terms have to do with how each block of data is stored by an audio program: most significant bits first (big) or least significant bits first (little). WAV files have always been ‘little endian'; originally AIFF files were ‘big endian’ but Apple changed to a new AIFF spec (AIFF-C) when they introduced OSX.

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