One of the most common requests that come into our Forensic Audio Lab is for Authentication. Has this recording been tampered with? Has something been added or taken away? Has the recording been enhanced making it more clearly understood now than it was before? In short, is the recording in its original form?
In most cases a digital footprint is left when an audio file is edited. If the file is an analog (tape) recording, we convert it to digital form and the footprint will still be there. We examine the file both audibly and visually and note any anomalies present. There are many things to look and listen for.
Sometimes they are easy to spot but some others are extremely subtle. Edits can be man made either intentionally or accidentally. They also can be mechanical or electrical. Knowing what for look for is the key.
Nearly always we call tell if a recording was altered and whether it was man made or not.
Here is a screen shot of a man made edit.
Here is a screen shot of a mechanical edit.