A louder, more dynamic passage will have a higher voltage output while a quieter one will have a lower voltage output regardless of the frequencies involved. "
True! Audio is "two dimensional". The voltage corresponds to amplitude or "loudness" (how far the speaker moves). Frequency is the how fast the waveform changes (how fast the speaker vibrates) and it relates to pitch. Low frequencies are bass and high frequencies are treble. With regular music, usually the lower frequencies are stronger than the high frequencies (although it may not sound that way.)
If it is, is this being measured in the CD Player reviews here on ASR?
Yes. Amir measures the maximum voltage. He also measures the voltage from DACs (analog-to-digital-converters)... and almost everything else.
If you open an audio file in
Audacity (a free audio editor), you'll see a waveform.
The image on that page shows audio with "maximized"
* positive and negative peaks. The scale on the left shows -1 to +1 which is the "normalized" level, where +/-1 is 100%.
The digital samples (44,100 samples per second with CDs) represent the positive and negative height of the waveform at one instant in time. If you zoom-in far enough in Audacity you can see the individual samples (
Digital Audio Fundamentals).
The DAC inside the CD player converts the samples to voltage. The analog voltage is filtered/smoothed to "connect the dots" to re-recreate the analog waveform.
Most CD tracks hit the digital maximum of 0dBFS. But if they are short in duration we don't necessarily perceive them as "loud".
There are some "guidelines" for
audio line level but there is no calibration standard...
Some CD players put-out more voltage than others. A volume control affects the voltage and the amplifier boosts the voltage (an current) to the speaker, etc. Once you've adjusted the volume everything is the same.
The speaker vibrates in-and-out in proportion to the negative and positive voltage, making sound!
Silence is a flat line. Digitally, it's a series of zeros. In analog silence is zero volts.
Normally we measure the level in decibels rather than percentage (Audacity's meters show dB.) Decibels need a reference and the digital reference is the digital maximum of 0dBFS (zero decibels full scale) so digital dB levels are normally negative. Loudness in the air is measured in dB SPL where the 0dB reference is approximately the quietest sound that can be heard so SPL levels are positive. Again, there is no standard calibration but there is a direct correlation. If you reduce the digital level by 10dB (a bigger negative number) the SPL loudness in the air also goes down by 10dB.
Program Dynamics (or I like the term "dynamic contrast) is
the difference or range between the quiet and loud sounds.
Dynamics come from the recording, not the CD player. Sometimes it's called "dynamic range" but I like to use dynamic range to describe the limits of the equipment (or format) which is limited on the quiet-side by noise, and and on the loud-side by how loud it can go without distortion.
Dynamic compression reduces the dynamic contrast by making the quiet parts louder and/or loud parts quieter. In practice, it's used during audio production to make "everything louder". Don't confuse dynamic compression with file compression (like MP3) which makes the file smaller without affecting the program dynamics.
* With regular (integer) digital files, 0dBFS is the highest positive and negative numbers you can "count to" with a given number of bits. A 24-bit file has bigger numbers than a 16-bit file but everything is automatically scaled during playback so the 24-bit file is not louder.
