A great question, well worth asking, so let’s discuss it.

You may not realise it but there are so many elements contributing to the sound of a CD player that no two models will ever sound quite the same. This is true of any piece of hi-fi equipment, and most other things, including guitars, amplifiers, radios, speakers, etc.

Ones and Zeros

When you play a CD, what you hear is the sum of many complex electronic and mechanical elements working together. A common technical misunderstanding concerning CDs is that:

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

Whilst it’s true that CDs contain digital data, ie ‘ones and zeros’, the statement above belies a lack of understanding of how the data on a compact disc is converted into music you can hear. CD players produce digital data streams that vary minutely from one-another. These variances can been and measured and that’s before we get the digital to analog conversion element which takes the data and converts it into an analog waveform we can listen to. This stage contributes more to the sound we hear from a CD player.

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, something which fascinates me.

The bottom line is that you can’t listen to ones and zeros. A complex series of signal decoding and processing steps have to occur before you can hear music from a CD. These step, along with all the different ways they can be done, variances in parts, circuit luxury, chipsets etc account for the distinct sonic differences between CD players.

The Devil is in the Detail

As with all things technical, there its so much more to know than most realise and that’s how misunderstandings like this originate. To retrieve sound from a compact disc, data has to be read from the disc, error-corrected, filtered and anti-aliased, converted from a digital bitstream into an analog signal we can listen to, amplified and buffered for sending it elsewhere.

There is no single way to do this and there are literally hundreds or even thousands of components between the disc and your ears, all contributing to the sound in subtle ways, and that’s just inside the player! There are innumerable combinations of parts and techniques to retrieve an audio signal from a CD ranging from less than $10 to house-like prices, and beyond!

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.

My Accuphase DC-91 for example represents one the most expensive and predictably best-sounding series of designs/parts/decisions allowing beautiful audio to be extracted from digital signals. This costs as much as a car.

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!

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.