During February 2020, Cheadle DATA Recovery Ltd performed a recovery for Dave Masterman, producer for BBC Radio 5 Live Elis James and John Robins show. They had lost three podcast recordings due to data corruption on an SD memory card. This happened because the audio recorder lost power mid recording. This, and CDR's involvement afterwards, is explained on the radio show (listen below, or via YouTube). An emergency 24 to 48-hour service was provided by CDR with a successful recovery. Full technical details of the SD card failure and the associated data recovery techniques can be found at the foot of this webpage - it proved a challenging case due to interleaving audio data.
This is Dave. Dave came from Manchester to London to record Elis and I doing an escape room. Dave carried all the kit. Dave has a dislocated shoulder. Dave spent two hours with us escaping from a room. This is Dave realising it hadn’t recorded. #PrayForDavepic.twitter.com/s1kNdbgCsf
To follow on from my former friend’s kind tweet about today’s audio disaster (@nomadicrevery), I thought I may as well now share with you the corrupt audio we have as a result. This will play in my nightmares for the next five years. pic.twitter.com/Kl9qsQWvLZ
The above tweet is about the corrupted audio which the radio producer had extracted by his own data recovery attempt. It is not a sample rate problem but instead relates as to how the specific audio recorder stores data to the SD card.
The portable audio recorder in use was a Zoom H4n audio recorder. This has the capability to record up to four audio streams simultaneously. It can be used with personal radio microphones so users can move freely whilst their individual voices are recorded. In the production edit, the separate audio files are played back simultaneously so that each person has the same level of volume.
File Allocation Table (FAT) corruption after power loss
The data loss was reported due to lack of battery power and the audio recorder suddenly losing power. As a consequence of this, the File Allocation Table (FAT) had become corrupt. On inspection of the SD card, it was clear that there were no folder or file name entries associated with the required data. Full sector-by-sector scans could not locate any reference to the required files in the FAT. The FAT defines the folder and filename structure, but also (critically) defines the location of files by LBA values and deals with any splitting of files if these are not written in sequential blocks in the SD card. Without the FAT it was necessary to perform a 'RAW' recovery and to locate files by file type (e.g. .WAV, .MP3 etc).
Interleaved audio streams
The garbled high-speed audio which can be heard on the radio show is because the recovery attempt made by the show's producer failed to take into account that the three audio streams were interleaved within the raw data. Whilst their 'RAW' recovery found the start of each file it could not take into account the method in which data was written to the SD card by the Zoom H4n audio recorder. Below are examples of working audio files from the Zoom audio recorder, which show this interleave between files.
Removal of the interleave
To obtain normal audio playback it was necessary to take each of the "RAW" .WAV files in the recovery, and then write a script to separate the three streams of audio. Essentially the first 64 sectors of data were extracted to create audio 'stream 1', the following 64 sectors of data to create 'stream 2', and the third 64 sectors to create 'stream 3'. This process was repeated over and over again until each of the three audio streams were fully assembled and would playback normally.
Partial recovery of the third podcast audio file
In the radio show, you can hear how the producer tried to "Wake up" the SD card by copying some additional data to the SD card after the data loss. The golden rule of data loss/recovery applies here: if you lose data turn the device off and do not attempt to use it. The audio recordings they wished to recover had not been marked as 'allocated' within the FAT. Consequently, when new data was copied to the SD card it wrote to areas of the SD card which contained the required data. Once data has been overwritten with new data there is no method to reverse this. As a consequence, it was only possible to recover the first 15 minutes of audio associated with the third podcast recording.
I'm very pleased with the service. I was sent regular updates on the progress, the prices were clear upfront and they were very quick to get back to me regarding any queries I had.
17:09 22 May 20
15:09 13 May 20
Excellent advice and assessment of the data issue I had. Very much appreciated.
12:27 08 May 20
My 1TB Seagate hard drive failed one day with a very unhelpful message at boot up saying 'SMART drive detects imminent failure : failing attribute #05 to minimise risk of data loss, back up the... contents of your hard drive and run DPS self-test in F10 set up'. How I was to back up my data I dont know as I could not get win10 to boot! I tried to get my data recovered myself using an online free programme called EaseUS. I spent many days going round in circles as the programme kept stalling. I did not know whether it was mechanical damage or a disk error. I looked online for good reviews and found Cheadle DATA Recovery Ltd as about 15 years earlier I remember giving my disk to a local computer shop and me getting the disk back and no data.I called John at CDRL and he explained it sounded like a non-mechanical problem so offered his less costly option. I also opted for the 7 to 9 working day service. Not cheap at £395.99 including new disk, courier service & VAT but according to reviews I was confident the costs would not increase whilst having a good chance of success.I was able to track the progress online from receipt, to initial cloning of the disk, to the folder and file structure being built. On working day 9 I received the file structure, confirmed everything was recovered, paid and I received a disk 2 days later.Turned out that the problem was disk errors that the heads could not by-pass and a firmware update was needed. i.e. I was never going to get any success via online programmes.I am very grateful to John for his skills and professionalism.read more