Audio Dropouts

Nothing in my opinion, is more irritating than audio dropouts.
Be it in music, speech or the sound track of a video, they are
extremely jarring and detract from the enjoyment.

Audio dropouts can be caused by many things, but usually
as a result of inferior/faulty equipment, buffer under-runs
or just plain sloppiness from who ever is recording the media.

They can occur on only one channel, both channels of a stereo recording, or even
all channels in a 5.1 or 7.1 surround sound recording.
The duration and "intensity" can also vary, making them not the easiest of things to remove.

This is especially true if the audio is part of a video's soundtrack, you can't just lop them off
otherwise the whole audio will become out of synch with the video.

If the dropout is only on one channel, copying the other (good) channel and pasting it in place
sometimes works, depending of course on the content, phasing and stereo field.

The other way of course is re-synthesizing it, from bits and pieces.
Slow going, but no real alternative.
That then, probably explains the clip below, from a well known broadcaster
who shall remain nameless. ;-)

Before, 5 dropouts in just 20 seconds, and it's not even the whole clip.

With a bit of effort and time, the result is much better and well worth it.

Next up..what lurks beneath

The Call of the Ibis

 The call of the ibis, summed up in a single picture:

Love them or hate them, the ibis must be responsible for countless ruined recordings.

According to Wikipedia:

What they don't mention is, these note have a glissando effect and are very loud, which in
turn creates loads of harmonics and can even overload recording equipment, causing clipping.

The ibis sound is then a perfect candidate to try some DSP on.
Let's make it even more difficult by having some music too.
The music has very simple notes, which makes for a good test and simple to hear
 if we change the "sound" or timbre of the notes in any way.

The "raw" recording:

PauloV · Ibis - Before

I'm pretty pleased on how it turned out.
The dreaded call of the ibis is 99% gone and the timbre is unchanged.

PauloV · Ibis - After - 1

Add some extra ambience and they are pretty much gone.

PauloV · Ibis - After - 2

It wasn't easy, took a bit of time but the result is worth it.
Can the call of the ibis be removed every time?

Probably not, or at least not 100%, but at least it's worth a try.

Better than scrapping the whole recording.

Next: Audio Dropouts

Enhancing old recordings

Let's start off with a recording from 1919.
The original was recorded by the Edison Company and is a short comedy skit.

As expected, lots of noise, limited frequency response and it's monophonic. 

When restoring and cleaning up old material, there is always an important question to be asked..
How much to clean up.
For these examples, I will restore to different levels, so as to better demonstrate what is possible.

Below, is the same clip, cleaned and a stereo field is re-created.

The judge is on one side, the bailiff on the other and general sound effects centered slightly wide. 

Here is another, a 1953 Elvis recording.

Usual sort of thing, noise and limited frequency response.
The recording was not badly made, it was the norm for the 50's.

Technology has moved on, and so has music and how it sounds.
There have been many studies on how music (frequency wise), has evolved over the decades.
Here is a graph showing the average results from thousands of songs across many genres.

Today's music has more low end, less mid-range and more high end by several dB's, when
compared to the 1950's.

So let's apply it to the 1953 recording.
Listening on good speakers or headphones is recommended.
Note how the guitar is richer, brighter and wider.

It's a tad too "bright" for my liking, but I intentionally left it like that to show what can be achieved.
The trick here, was to re-create the high frequencies that were non existent in the original.
Simply using EQ is not going to do that, as it will just amplify more noise.

One more example, a LM radio special broadcast for New Year's eve, 1969-1970.

Since it was recorded off a shortwave radio, there is plenty of noise, crackles, whistles and heterodynes.
The original is barely listenable due to a constant whine and carrier heterodyning with other stations.

After much processing as there where plenty of interfering sounds and carriers, we have something

much more pleasant whilst keeping the characteristic shortwave "sound".

Next Post - The call of the Ibis