Archive for the ‘GNU / Linux’ Category
High resolution audio and video digital tape conversions can use large amounts of computer storage. 8 bit uncompressed Standard Definition (SD) PAL video runs at 70 GB per hour and 24 bit 96 kHz audio files at 2 GB per hour.
As a result of this many of our analogue to digital tape transfers require the use of external storage, usually USB 2.0 portable hard drives, to supply the copied digital transfers back to the customer. Some drives supplied by customers have not been of great quality and not designed to be sent about in the post. One such drive we had recently, a Sony Vaio branded 2.5″ USB drive wouldn’t copy certain directories of important files with the Mac OS Finder or the Windows Explorer. While most of the drive copied this certain folder always resulted in a crashed computer!
Thanks to GNU/Linux we have a bit more power and information at our disposal about hard drives and IDE or USB interfaces. It’s always best practice to copy as much information from the drive or mirror it before attempting any other types of data recovery or file system repair. Using the standard dd
One of our recent and ongoing jobs is a very large, over 2000, NAB 10.5 inch reel to reel archive of quarter inch professional tape recordings.
To fit into the budget but maintain quality we needed to find a way to streamline our workflow in converting the high resolution 24 bit 96 Khz master .wav files to CD quality (16 bit / 44 Khz) and MP3 (320 kbps) audio files.
Typically this would be done manually with 2 track audio software such as Audacity, Peak Audio Tools, Wavelab, etc with a Graphic User Interface (GUI). For such a large amount of individual files this is time consuming, expensive and unnecessary. While many audio editors have batch processing tools, Amadeus Pro being one of our favourites, they are still not as flexible as combining command line tools with a Bash script.
SoX is a powerful command line audio tool that can be used to edit, convert, process, record and play a wide range of digital audio files. It also has a very high quality resampling algorithm which we are using here.
Once the tape reels have been digitised they are split into individual .wav files which are then renamed with artist and track details using a php script that accesses a .csv file. These 24/96 resolution files are then converted to lower, CD resolution using SoX and to 320 kb/s MP3’s using LAME. The script also uses sed, the stream editor, to add the text _16_44.wav or _mp3.mp3 to the filename for ease of identification. The script finds all files with the suffix _24_96.wav in all the subdirectories of it’s working directory and processes these.
At the moment this script is running under Mac OS X 10.5.8 using the MacPorts project but will, in time, be moved to one of our Apple G4 servers running the PowerPC version of Debian GNU/Linux 5.05 ‘Lenny’.
Not our normal type of post but the new HTC Desire Android smart phone has been so useful with it’s open source applications, fast speed and wifi that I couldn’t believe I’d just put the phone in my shirt pocket and leant over the toilet!
Panicking, I fished it out and messed about trying to shut it down, when I should have just whipped the back off and the battery out. I did manage to get the battery out pretty quickly but not before I’d seen the screen start to make weird colours and odd lines. The thought of buying a new phone at full price was too much so I pulled out a handy bottle of Isopropyl alcohol (IPA) we use for cleaning tape and video record and repro heads. This is 99% pure IPA, not cheaper ‘rubbing alcohol’ that is often 70% IPA with 30% water. You really don’t want to make your phone any worse!
When I’d calmed down a bit I checked the moisture pads that show if the phone’s had water contact. These had gone pink confirming the toilet dunking so no warranty repairs here! Having little to lose I removed the 4 small torx head screws and the two even smaller crossheads screws under the rear cover. Two of the Torx screws have ‘void’ stickers over them so again once you undo them you’ve lost your warranty!
Now the bottom cover over the USB connecter can come up as can the inner cover which will reveal the wifi / bluetooth aerials. I didn’t remove the screen but ‘carefully’ poured IPA all over the bits that smelt of wee!
99% pure IPA will evaporate very quickly but any residual moisture should go before you can think about putting the battery and other cards back in. Many online sources recommend uncooked rice to absorb moisture but purpose made desiccants are best. I used several silica gel sachets in a freezer bag with the disassembled phone and left this overnight.
Thankfully this all worked, the phone starts, the screen works it’s alive!
The key points when you have this kind of phone disaster are:
- Get the phone out of the water / wee
- Get the battery out as soon as possible
- Remove all the SIM / memory cards
- Shake or carefully pat dry as much liquid as you can
- Any liquid contaminant that isn’t pure water and contains sugars or salts must be cleaned off
- If you try IPA make sure it’s high purity 99% is best
Finally, we’re tape transfer specialists not phone repair specialists so I offer no guarantee with all this but it did work for me.
We’ve been honored recently to have won a large contract to help in the digital migration of an extensive educational video archive by the transfer from U-matic archive copies to uncompressed video files.
While the archive had been stored in an suitable environment and rarely if at all played, they had not survived well. The Sony branded tapes from the 1970’s and 1980’s all exhibited binder hydrolysis or sticky shed syndrome. We were still able to get good transfers though using our range of umatic machines, particularly the Sony BVU-950P and For-A Time Base Corrector.
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