Preserving Audio Quality
Knowing that I will be getting a difficult recording for audio cleanup in the first place, I try to preserve the quality of the recording as much as possible.
Uncompressed Format
The best quality digital format is “uncompressed PCM”, such as a WAV or AIF file. These are very large (10 MB/minute for a stereo file) and as a result are almost never used as the format for a digital voice recorder. Voice recorders and cell phones rely on clever algorithms to reduce the size of the recorded file by REMOVING frequencies that it calculates won’t be heard. This results in a file size that is roughly 10 percent of the original.
One way to understand it is that you can record 10 times longer - hooray! Another way is that you are now missing 90 percent of your original information - uh oh! Editing one of these files is like blowing up the picture you took with your cellphone to the size of a billboard. While I can’t get back that missing 90 percent, I can at least ensure that the recording isn’t further degraded during the editing process. The first step then is to convert to an uncompressed format before processing.
Device Transfer
Many digital recording devices have a USB connection that, when connected with a computer, allows it to be read like any other storage drive. The files on the device can be easily copied to a hard drive in order to be sent to me. This is the best method for transferring files, if it is available.
Other devices have a proprietary software application that is used to convert from the native format to a more widely used format. In those cases, the original device is needed to make the transfer and then convert it using the highest quality that the conversion software can give. From there it will be upsampled to CD quality before beginning any audio enhancement processes.
If the device does not have a USB connection available, the next best method is to send the audio out of the earphone jack to the line input of the computer or audio interface and manually record it in real time. Computer sound cards vary greatly in quality - poor convertors can add even more noise in the transfer process. I am using very high quality analog to digital convertors and transferring at a better-than-CD quality bit depth to ensure that the smallest details are preserved..
Portable Drives
If the recording is delivered to me as data files on a flash drive or CD/DVD, I will first check to make sure that the format of the files is CD quality. If not, they will be converted to 16-bit/44.1kz WAV files.
Physical Video Discs
If the audio is part of a DVD or streaming video, the audio will be separated from the video, and after audio cleanup, recombined back with the video.