I grew up collecting and listening to vinyl records. To me, they represented a baseline level of audio quality. So you can imagine my anticipatory excitement when I first heard about a new format called compact discs. The stylus would be replaced by a laser beam that read digital information from a small silver platter – no physical contact meant no more ticks and pops, and no more wear. A compact disc would last forever, and even the 1000th play would sound exactly like the first.
I still remember that defining moment, when I bought my first compact disc in 1985. I bought it before I even had a CD player, and for a couple of weeks, all I could do was gaze at it, mesmerized by the high technology contained within it, and then hold it up to the light and admire the diffracted rainbow patterns. That disc was Brothers In Arms by Dire Straits, and it sounded phenomenal There was no surface noise any kind – just music arising out of complete silence. The clarity was astounding and the dynamic range exceeded anything that I’d ever heard on a vinyl album. The only thing that surpassed this experience was listening to it through headphones. I had a pair of Koss SST/6s at the time, and when I turned up the volume, I was transported to another world – or at least into the recording studio with Dire Straits.
A few weeks later I bought another compact disc. They were expensive back then, averaging $18-21 each (I was still a student, and after spending $599 on the player, I didn’t have much money left). It was a classical and movie theme sampler CD called Time Warp. This disc had some additional, recently-recorded (DDD) material that took advantage of the 96 dB dynamic range of this new medium. In fact, this disc even had a warning printed on its front cover.
Fast forward to the present day. I still buy CDs regularly but many of the CDs that I have bought during the past decade sound agonizingly bad. This is not a commentary on the musicianship of the bands or the talents of the vocalists – that would require another blog post – but one strictly on the quality of the audio. Am I the only one who has noticed this? Is this something that’s noticeable only by people who have been listening tor CDs since their inception? If this sonic deterioration isn’t merely a figment of my imagination, then why aren’t more people complaining?
One CD, Vapor Trails by Rush (released in 2002), stands out as a particularly good (or bad) example. I could barely listen to it, because it sounded so horrible. It wasn’t the music – I like Rush; I enjoy their performances and own about 6-7 of their CDs – it was the audio quality itself. Their old 1970s and 1980s albums (on vinyl and CD) sounded great, and since that time the band members have matured as musicians. I was expecting great things from this CD… so what happened?
I decided to do a little investigative work, and started listening to CDs released in different decades. One thing I noticed fairly quickly was that the early (1980s) CDs were a lot quieter than my more recent purchases. Over the years, it seemed like the average recording levels have steadily increased. To test my theory, I decided to rip some songs and then examine their wavefiles in an audio editing program. When I saw the waveforms, I realized what was happening, and I understood why today’s music often sounds so terrible.
Here is the waveform of a song from Brothers In Arms, called Your Latest Trick:
Admittedly, this is a subdued, easy-listening song that borders on mellow jazz, which is why it’s recorded at a fairly low level. Here is the waveform of one of the loudest songs on this album, Money For Nothing:
Now let’s compare this to a song from Vapor Trails. This one is called Ceiling Unlimited:
As you can see, the volume level of this 2002 CD is substantially higher than Dire Straits’ 1985 recording. In fact, the sound waves appear to go right off the chart. There is an unintended irony in the song title, Ceiling Unlimited. Unlike analog audio, there is a limit to the dynamic range (the difference between the loudest and softest sounds) on a CD, which means that there is volume level ceiling. All audio recorded to a CD must fall within this 96 dB range. If you set your recording levels too high, then you will create what’s known as “clipping distortion”.
So, what exactly is clipping distortion? If you’ve ever had to squeeze your feet into shoes that were a little too small for you, then you’re already familiar with the concept. It’s a type of distortion that’s caused by a sound wave that’s deformed (or squished) because it too big for its “container”. If you view a recording (or in this example, a pure tone) on an oscilloscope or in an audio editing program, you’ll see something like this. The left image is of a soft tone, and the right image is a louder tone.
Since compact discs have a finite dynamic range, there is an upper limit to these waveforms, represented by the top and bottom of the graph. If you keep increasing the volume, then the edges of the sound waves will touch the edges of the graph. If you are an irresponsible audio engineer and increase the volume further, then the edges of the waves will extend past the graph’s boundaries (below, left). If this happens, then the part of the wave beyond the upper limit of the graph is clipped, and the maximum graph value is substituted for whatever the wave data might have been. The clipped wave looks something like this (below, right).
Now we have a strange hybrid shape that still looks more or less like a sine wave, but also contains the hard edges of a square wave. The result no longer sounds exactly like the source material. The more amplified the waveform is, the more of it will be chopped off, and the less the recorded waveform will resemble the original. The result is no longer faithful to the original sound. As you probably know, the Latin word for faithful is fidelis. What is recorded onto the CD is now something less than high fidelity.
To be fair, not all genres of music are affected equally. The loss of fidelity will not be as noticeable in electronic music. Synthesizers often use square waves or even triangular waves to generate sounds, so the clipping will not affect a note’s timbre as much as a sine wave. Kraftwerk could release an over-amplified CD and it’s likely that no one would ever know, unless they actually ripped it and looked at the waveforms. However, voices and all acoustic instruments generate sine waves, and these are the sounds most affected by clipping distortion.
I’ve also noticed this increase in recording levels on re-released and Greatest Hits collections. I bought Steve Miller’s Book Of Dreams CD, and a few years later I bought his Young Hearts Greatest Hits compilation. I was disappointed with the sound quality of Young Hearts, and thought that Book Of Dreams sounded clearer and less muddied. Here is a side-by-side comparison of the waveforms for Jungle Love – a song that is on both CDs:
Recording at a low level is, in my opinion, always preferable. If a CD is recorded at a low level, then you can always increase the volume on your stereo or MP3 player, or you can select “normalize volume levels” when you rip your CD and convert it to an MP3. Unfortunately, if the music is recorded at levels that are high enough to clip the tops and bottoms of the waves, then the source material is damaged (or even ruined). You could decrease the level in an audio editing program, but then you’d merely have a quieter version of the same clipped wave.
The thing I find disheartening is that we were doing everything properly right from the beginning. When CDs started to become popular in the mid-1980s, we were making new recordings and transferring existing material with the utmost care. Over the years, the recording levels kept increasing until they exceeded the upper limits of the medium, yet no one seemed to notice that the sound quality was suffering.
In conclusion, I’d like to share some Lion King-esque advice. When I was a teenager, my parents were always telling me (usually unsuccessfully) to “turn the music down!”. At the time I swore that I would never turn into my parents, but it turns out that their advice was sound. Therefore, my advice to studio engineers is the same: Please lower the volume – all of your time, effort and energy will be for naught if you insist on overdriving the equipment. Maintaining moderate recording levels will eliminate the clipping distortion, and give us back the high-quality music that we used to enjoy!