What You Are Listening To

So, here you are enjoying an evening, listening to your favourite music on a nice sound system and fully enjoying every minute of it. But, have you ever wondered what's going on behind the scenes?

"What exactly am I listening to?"

The answer might surprise you.

So let's take the journey from live performance, to microphone, to mixing and mastering, to storage, to distribution, to your system and finally to your speakers and find out exactly what it takes to produce such good music.

What is sound? Home Top Chapters

Sound is small fluctuations in air pressure. Since changes in pressure cause motion, the sound breaks away and travels through the air. This is sometimes depicted as waves. But the complexity of it is more like waves on a beach than the simple waves you see on an oscilloscope.

The amount of pressure change translates to loudness, big changes are louder than small ones.
The rate of change translates to pitch, the more often the pressure changes, the higher the pitch or frequency of the sound.

As the sound radiates out and the air pressure at your ear fluctuates it moves your ear drums. They signal your brain, which in turn interprets this motion as sound.

The pattern of these fluctuations is complex enough that things sound different to us. A bell does not sound like a guitar string. We remember these patterns subconsciously so that we can recognize various sounds and by the time we reach maturity we will have a very high success rate at identifying various sounds, particularly voices and musical instruments.

What is music? Home Top Chapters

When you are listening to a live performance of natural instruments what you are hearing is the specific sound of each instrument creating its own wavefront that eventually reaches your ears. In your ear, the resulting pressure changes are summed into one very complex motion of your eardrum that you will hopefully interpret as good music.

Thus, music is multiple sounds from individual instruments.

Capturing sound Home Top Chapters

In order to capture a musical performance in some reproducible way we need to "hear" it and store it. This is where we use microphones.

A microphone is a type of transducer. Transducers change energy from one form to another, in this case from sound waves to electrical signals.

When a sound wave passes a microphone, the changing air pressure will cause its diaphragm to vibrate in much the same way as your ear drum. The microphone's internal mechanism changes this vibration to a continuously updated electrical signal that fluctuates in voltage in step with the air pressure. The output from the microphone is thus an electrical analog of the motion of your ear drums.

In a typical recording session one of two things happens. Either the band plays the music with multiple microphones arranged to capture their performance or, in a studio session, each musician plays in a sound booth and the microphones capture that performance on its own.

From this point on, the performance is not sound anymore. Now it is a group of rather complex electrical signals that vary over time to mimic the air pressure changes of the live performance.

Storing the signals Home Top Chapters

Now that we have our signals, we need the means to store them. This is typically done by first passing them through a mixing console that adjusts the levels to those suited to a recording device. Then the adjusted signals are sent to a multi-track recording device for storage.

In the early days of recording, these storage systems were using magnetic tape. The signals were stored as tiny changes in magnetic flux on the moving tape in a pattern that again mimics the changes in air pressure heard by the microphones. But now with everything going digital, the storage device is most often a computer. In this case the electrical signals from each microphone are converted to a series of digital samples representing the level of the signal over a very short period of time (typically 1/48,000th of a second). These samples are then stored in data files that are not unlike any other computer data.

Mixing and mastering Home Top Chapters

The next step along the road is taking the stored information and massaging it into something more compatible with home entertainment systems. Along with combining multiple tracks into two, for stereo, this can include considerable modification of the recorded data itself. It can be equalized, compressed, limited, panned and any number of other tricks to give a better result on a home system.

It is worth noting that the stereo image you hear on your system is set into the recording at this point. Some sounds are moved to the left, some to the right, some are kept at centre. This gives the "soundstage" illusion as you listen from your sweet spot and it is totally under control of the audio engineers working on the recordings.

Along with left or right panning, the overall tonality of the recording is set at this time. Whether a song is shrill, shouty or bassy is again completely under the control of the recording engineers.

Finally, once they have a completed version of what they want you to hear, the final mixdown and master recording is ready for distribution.

Going to market Home Top Chapters

At this point a stereo recording exists in 2 channels. Each channel presents a single highly complex waveform that changes over time. Now the problem is to distribute this to the masses for their enjoyment.

The final product is then mass produced and readied for its fans. Distribution can take place in any number of forms. Tape, Vinyl, CDs and Digital files have all been popular in their times. The current trend is toward streaming audio from the internet.

In analog systems, these waveforms are most often represented as either small changes in magnetism on tape or wiggling groves on vinyl records. In digital formats, they are represented as dots and dashes on CDs or as samples stored sequentially in digital files.

Definition of High Fidelity Home Top Chapters

So now we have our two waveforms on a stable platform. We can reproduce them in our homes. This is all good. But, before we go much further we need to understand a couple of mildly technical points.

First, we need to appreciate that the physical distribution does not contain sound nor does it contain music. It simply contains encoded versions of two constantly changing complex waveforms.

Second, we need to know that the goal and definition of "high fidelity" is to amplify and reproduce these recorded waveforms as accurately as possible.

Be sure to note that this does not extend back to the original performance which has surely been modified heavily in the process of preparing it for distribution. In fact, sometimes what you hear at home bears very little resemblance to the original performance of a song.

Inside your system Home Top Chapters

In your home system, the first job is that of decoding and recovering the recorded waveforms. This can be done either by mechanical means as with vinyl records, magnetic means for tape recordings, optical means for CDs and DVDs or by mathematical means for computer files and streams.

Now we get to the reason that an entire musical performance has been reduced to just one or two waveforms. It is a basic law of electrical physics that any conductor (wire, circuit, etc.) can only have one voltage present at any given point in time. You can't pump twenty separate instruments through an amplifier. But you can push through a single waveform that represents the sum of their sounds.

Thus, the goal in all your audio equipment is that of amplifying this single pair of waveforms from your recordings to a level that can successfully drive our speakers.

And that brings us to the final step in the journey.

Making sound Home Top Chapters

Up to now we have been following an electrical signal. But we can't hear electrical signals, so we need the means to convert those signals into something we can hear. This is where our speakers come in.

A speaker is basically a linear electric motor with a spring return to centre position. It acts as a linear positioning servomechanism. With a cone or dome attached, it can push air and acts as a transducer that changes electrical signals into changes in air pressure.

When you apply a voltage with enough current, a speaker will move its cone in or out by a distance dictated by the voltage applied. Changing the voltage will change the position of the cone. If we do this rapidly enough we can move enough air to make sound waves. If we do it accurately enough we can produce highly complex sound waves like those in the waveforms in our recordings.

In the end, the waveforms we recorded with such care are just a map of how to move the speaker cone. Your amplifier and other equipment simply gives it enough power and then feeds it to your speakers which convert it to sound.

Now, for the first time in our journey through all these steps there is something we can hear.

Summing up Home Top Chapters

As we established early on, music is the sum of several discrete sounds originating from multiple instruments. But, that is not exactly what is happening in your home stereo system. What you hear is the result of two electrical waveforms each applied to one speaker. That is not music.

The good news is that when all this works right, you get a really enjoyable approximation of your favourite music.