- Whether I can Edit (Removing Hisses, Distrtions,cleaning, removing unwanted noises etc.) those with AUDACITY at this point?
If the recording is very-bad, there’s not much you can do and often "the cure is worse than the disease". Pros still record in soundproof studios with good equipment (and good talent). On-location movie-dialog is re-recorded in the studio… Even pro audio software cannot take a poor recording and make it as good as a pro studio-recording.
[u]Noise Removal[/u] can work very well if you have a constant low-level background hiss. In other words, it works best when you don’t really need it. It’s almost always worth a try, and if you get artifacts (side effects) that are more annoying than the noise, you don’t have to use it.
Of course, you can “manually” mute, lower the level, or edit-out any sound you want. But, you can’t generally separate or “un-mix” sounds. So, if there’s a dog barking while someone is talking or singing, you won’t be able to remove the barking without also killing the singing/talking. Or, if there’s a noise in the left channel you can mute the left channel, and you can even copy the right-channel signal to the left for that period of time… That stuff depends on how much time you want to spend.
Sometimes the Equalizer or a filter (high-pass, low-pass, or notch) can help to to remove/reduce noises at a particular frequency/pitch. But of course, this usually also affects the good sounds that you want to keep. Usually, the best approach is just to “play around” with the equalizer to see if reducing a particular frequency-range helps. Once you’ve “zoomed in” on a particular frequency range, you can try a regular filter for a more-drastic effect.
A high-pass filter let’s frequencies above the cut-off frequency through and reduces lower frequencies. A low-pass filter leaves the low frequencies unaffected, and reduces high frequencies. A notch filter knocks-down a narrow range of frequencies. For example, if you have 50 or 60Hz power-line hum, a 50/60Hz notch filter will kill it without affecting higher or lower tones.
Distiortion is generally impossible to remove. Audacity does have a Clip Fix tool (effect) that attemps to correct distortion cause by clipping (“overload” distortion).
- Can I do so during or at the time of Burning DVD’s?
It depends on what software you are using. Most video editors have some limited audio editing capability. But, it’s common (especially for professionals) to use separate audio editing software. As long as you don’t do anything to affect the timing/sync (like cut-out a section of audio) this usually works fine. All video editors (and most DVD authoring applications) allow you to import a new/different/edited audio track.