Why don’t all CD players sound the same?

There are so many elements inside a CD player contributing to the sound that no two CD players will ever sound the same, except perhaps two of the same model.

When you play a CD, what you hear is the sum of many complex electronic and mechanical elements working together. This of course applies to any piece of hi-fi equipment, and beyond that to anything really, including guitars, amplifiers, radios, speakers, etc.

Ones and Zeros

A common technical misunderstanding concerning CDs is that:

“It’s digital, it’s all just ones and zeros, things HAVE to sound the same.”

Many people

Yes, CDs contain digital data, ie ones and zeros, but this statement belies a profound misunderstanding of how the sound gets converted from binary words on a compact disc into music you can hear. It also demonstrates no awareness of the variances in digital datastreams CD players produce, and that’s before we even get the digital to analog conversion, which contributes more to the sonics.

Even different CDs of the same recordings don’t sound quite the same in some cases, a story for another FAQ. Likewise, CD transports only extract the digital data from the disc, yet they sound different. The bottom line is that you can’t listen to ones and zeros and an enormous amount of signal processing has to happen before you can hear music from a CD.

The Devil is in the Detail

As with all things technical, you don’t know what you don’t know. Data has to be read from the disc, error corrected, filtered and anti-aliased, converted from digital into analog, amplified and buffered. There are hundreds of components in the signal path between the disc and your ears and hundreds more contributing to the sound, and that’s just inside the player!

Op-amps contain dozens of components and there may be several different op-amps in the signal path! It is worth noting however that CD players have less immediately obvious differences than some other sources and that it takes some experience to be able to describe these differences, at least initially.

Even CD transports that lack any form of DAC can sound dramatically different from one another. I’ve written an entire FAQ about this topic!

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My precious…

The Sum of the Parts

Each of these elements contributes to the sound of a CD player, along with others I’ve probably forgotten:

  • The CD mechanism or mech, spindle motor and laser
  • The hardware carrying the RF signal – shielded coax or unshielded wire, connectors, termination impedances and reflections
  • DAC type and design – R2R/multibit delta-sigma/chip/discrete
  • Analog and digital filter type and design – HDCD/FPGA/DSP/none
  • Device firmware running the digital filters, PICs, FPGAs etc
  • Inter-stage analog amplifiers and buffers, op-amps
  • The all-important output buffer – discrete/op-amp/class-A/tube/transistor/transformer/balanced/singled-ended etc
  • Power supply – linear/SMPS, filtering details, regulators, wiring
  • Clock – frequency/PPM precision/drift/stability
  • General layout, board design, wiring, shielding, parts quality
  • Condition of the unit, laser power output/health, general state of service
  • Vibration isolation differences between players and isolation hardware

CD players are complex mixed-signal (digital and analog) hardware devices. Unsurprisingly, they sound different, just as turntables sound different.

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