A Hum-ble Audio Limerick

by Peter Utz
November 2001

An audio expert named Jones
Was praised for his mastery of tones.
Before every shoot
The wily old coot
Would slip on a pair of headphones.

For over the years he had learned
A sure-fire way to get burned,
Is assuming the best
With never a test
'Til after the party's adjourned.

So always he checks out his sound,
`Cause once in a while he's found
A buzz or a hum
That's most worrisome
Lurking fiendishly in the background.

Let's all get inside Jonesey's mind
As he thinks through the problem assigned
And take some insight
If his technique is right
And go home with our talents refined.

Recorders and mixers, whatever,
Will always possess this one lever:
Master volume control
Turned down very low
Should cancel all sound whatsoever.

If it doesn't, your amp may be shot.
Its power supply's not so hot.
The hum that you hear
Shouldn't cause any fear.
Your recording's OK, is it not?

To be sure, you could make a test tape.
Play it back and then pause it agape.
If the hum doesn't change,
Then nothing is strange.
Your recording is fine and shipshape.

However, if turning down "master"
Makes the hum become less of a blaster,
It may be upstream.
So we set up a scheme
To look there for our noisy disaster.

To narrow the hunt we've begun
We lower each source one-by-one,
And finding the culprit,
Proceed to unplug it
To see if the noise is undone.

If silence is what we restore,
We narrow our search even more.
It may be a cable,
And if we are able,
We bypass the wires galore.

Connect up the source most direct
To see if the sound is correct.
If it's better, we know
That the wire must go
To the workbench for cable-dissect.

But if the source still makes a hum,
Connected with wires minimum,
Then the source, my good buddy
Is where we should study,
A process not too burdensome.

If powered, then turn off the juice
And wait for the noise to vamoose.
If it does, then assume
It's the source of your gloom.
The problem becomes less obtuse.

A source with its own headphone out
Lets you plug in your phones there to scout
For where the noise entered.
Your search is now centered
That's what troubleshooting's about.

But what if this source sound is clean?
Only hooking it up makes it mean.
Go back to the cable.
It's good, but not able
To handle a ground loop unseen.

Now what is a ground loop you ask?
And why does it confound our task?
They're signals that travel
Through soil and gravel,
In ground shields, AC cords, they bask.

A ground loop you often will start
When you plug in two items, apart.
Each gets its AC,
But their volts disagree,
Making signals on ground wires dart.

A solution to try at the outset:
Plug all of your gear to one outlet.
The grounds will be same,
Your hum problem tame.
Continue recording with no-sweat.

But sometimes this trick doesn't work.
S'no reason to feel like a jerk.
It's back to the wire,
Your main source of ire,
To try out some more handiwork.

If unbalanced lines are your trade,
(One conductor, one shield, they are made),
With plugs RCA,
Phono, phone, mini, hey,
You're asking for trouble brigade.

These wires aren't meant to go far.
The things they pick up are bizarre.
Even in good condition,
Their poor sound rendition
Will drive you to drink at a bar.

They may work OK if they're short,
And high level signals transport.
But you're bound to say "yikes"
If you use them for mikes,
'Cause low-level signals they'll thwart.

When using an unbalanced line,
If you hear a loud buzz, it's a sign
That the ground has come loose.
Check the plug, silly goose.
The shield came detached at the spline.

Professional work is your thrust?
Then balanced lines must be discussed.
Their three-wire system
Takes hums and enlists 'em
To cancel themselves into dust.

These wires have lower resistance,
Are useful for quite a long distance.
For mikes, they're a charm,
Never causing a harm
To your sound; they excel with persistence.

But now for a trick of the trade.
When balanced connections are made
'Tween mixers with power,
Your sound will go sour,
Unless some attention is paid.

Remember the ground loop decree?
Watch out for all gear with AC.
When used in cascade,
The ground loops invade
And cause a hum/buzz jubilee.

Now if your good sound runs amuck
With all balanced lines you're in luck.
By detaching the ground
You'll not damage the sound.
The ground loop will stop like "the buck."

When lifting the ground shield, my friend,
Be sure to lift only one end.
Thus the wires inside,
Stay protected with pride,
And sweetest of sounds they will send.

If cables have grounds wired-thru,
There's still a solution for you.
Attach a ground-lifter,
A plug that'll shift-er,
From unending ground, sans ado.

That surely should cut out the hum.
The technique is not cumbersome.
With a quick disconnect,
You return to direct.
Such arrangements are not always dumb.

Don't use this ground-lifting convention
With your mike or mike cable extension.
Ground them all the way thru,
To further imbue,
The best interference protection.

And now for a final detail.
It's a problem we often assail.
Where do you begin
With an unbalanced in
Where balanced lines elsewhere prevail?

Solution to make your heart warmer:
We plug in a matching transformer.
It changes the kind
Of the signal you find
To the other or back to the former.

Transformers are used near the source,
Near input or output of course,
So now the long wire
Stays balanced entire
Hum bucking with maximum force.

When Jones has done everything right,
He still could be in for a fright.
We know Murphy's Law
Will side with the flaw.
On playback, the hum-bug could bite.

The damage is already done.
Removing it never is fun.
A filter's required,
Parametric, or wired
To graphic EQ-either one.

And now your dear tape is played back.
Your filter is tuned to attack
The tone that offends.
Its volume descends,
But fidelity's all out of whack.

You never get something for naught.
Your sound will be worse than you sought.
At least it is clear.
What's vital, you'll hear.
Who knows, you may never be caught.

My poem is just about through.
And probably just in time, too.
Save your feathers and tar.
It's just something bizarre
From Videomaker to you.

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