We’ve been involved in a couple of projects recently where there is confusion about file formats and compatibility with Windows Media Player (WMP). Specifically, one of the most common types of digital audio file extensions is the “.wav” extension, which is GENERALLY playable in all the standard media players like WMP, iTunes, RealPlayer, etc. The .wav extension has become more or less a “standard” if such a thing exists in digital audio.
But the truth of the matter is quite a bit more complex, and can make your projects more challenging if you are not aware of it. In reality, the “.wav” extension merely defines a “wrapper” for an audio file, and tells whatever media player you are trying to use certain information about that file. This information can vary considerably, but the most important thing it tells is what codec was used to create the actual digital audio track.
What’s a codec, you ask? Well, that is an industry abbreviation for the “coder-decoder” that was used to capture the analog audio and convert it to a digital signal. Every digital sound file has gone through a transformation, from the original analog sound waves to a series of bits and bytes that are generated to capture that sound wave and then recreate it through the computer. The original capture and digitization of that sound is the coding part, and the subsequent processing of that code to play it back out of a computer (or CD player, DVD player, etc.) is the decoding part. And there are many different codecs that can be used to accomplish this task.
One of the oldest and most common codecs is PCM (pulse code modulation), which is the standard for capturing and playing back audio from computers, CDs, etc. But while PCM can produce a nicely accurate rendition of the original sound, it tends to be very “uncompressed” which means the digital files it creates are quite large. In order to solve for the problem of file size, and still retain fidelity in different regions of sound, different codecs have sprung up to handle different types of audio. For example, MP3 was developed specifically to retain a higher fidelity of sound for music, but at the sacrifice of keeping fidelity in the sound ranges represented by normal speech. Similarly, the telephony industry has developed certain codecs to maintain adequate representation of normal spoken content but to reduce the fidelity of other parts of the sound range to save file space. (The more educated reader will recognize that I am glossing over the issue of sampling and its effect on file size. For those that are interested, go to this this Wikipedia page.)
But here is the crux of the matter, and the trouble you may run into with an audio discovery project. The “.wav” envelope can contain audio files in any number of different codecs, and these codecs are not all playable in WMP…or any other standard player. The reason for this is that not all codecs are freely licensed. Some codec developers have put restrictions on their creations, requiring that anyone wanting to play files in this format have a license to do so. And since Microsoft (and Apple, and Real) don’t feel like paying millions of dollars to these developers for each copy of WMP (iTunes, RealPlayer, etc.) they distribute, then these codecs are not recognized by those media players. And thus, you have a .wav file that you may not be able to play.
Since audio discovery is most commonly about reviewing telephone calls, you are likely to run into two of the codecs that have become popular in telephony, due to their file compression and voice fidelity characteristics: TrueSpeech and G.729. And while these files will commonly come with a .wav extension, you will get a nice little error message from WMP when you try to play them. Two things to keep in mind when you are dealing with files of this nature:
- You must make sure your audio discovery vendor has the ability to deal with them natively so that you can accomplish your review; and,
- You must also make sure that your vendor can convert any of these files that you need to produce to regulators or opposing counsel. Otherwise, you are likely to get a pretty nasty response (or worse!) back from them if you’ve delivered files they can’t play.
If you would like to know more about file formats, or learn about Nexidia’s ability to handle these (and just about any other) formats then please visit our website or reach out to me directly. We can make sure you can surf the .wavs without wiping out.
One of the first challenges you have when faced with an audio discovery project is determining just how much content you’re dealing with. In the rest of the e-discovery world, this is measured in gigabytes of data. That works okay, because with emails and word documents, even TIFF documents, there is a generally understand correlation between gigabytes and the number of pages in question. And this translates into the general work effort you’ll need to go through it all, either with or without a technology assist.
But audio and video are time-based media, and should be measured as such. Again, knowing how many hours you have to sift through will greatly determine the method you choose to perform the discovery. And the problem is that there is no easy correlation between file size and file length. Why not?
The answer is “bit rate.” Loosely translated, bit rate defines the number of bits that a given recording system uses to capture the audio and put it into the digital file. Bit rate is usually measured in Kbps, or kilo-bits per second, and can vary widely from 8Kpbs up to 128Kbps or even more.
If you hear people talk about “compression schemes” this is what they are referring to. Audio that is 8Kbps is much more highly compressed than 128Kbps. To illustrate, one Gbyte of audio encoded at 8Kbps contains 277 hours, while one Gbyte of audio at 128Kbps is only 17 hours. You can see from this example that gigabyte pricing for audio projects can have little relation to the amount of audio that you will have to review.
So the next time you are faced with a big project and your client (either internal or external) says “I’ve got 100 gigabytes of audio we need to review” you can be prepared to ask the most important follow up question.
“Okay, do you know what the bit rate is?”
They may not, but this at least starts the conversation down a different path, so you can jointly determine the number of hours in the project which is what really matters.