What is Hi-Fi?
In the pro audio / audiophile community, certain traits are consistently identified with the hi-fi (high-fidelity) label.
For me, performing speaker and room measurements has recently clarified what these traits are.
Tonal range #
The accepted tonal range of human hearing is 20 Hz - 20 kHz. This can be thought of as four ‘decades’: 20 - 200 Hz, 200 Hz - 2 kHz, 2 kHz - 20 kHz.
In musical terms, doubling the frequency raises an octave. Starting instead at 16 Hz, which is the lowest pipe organ note, shows eleven octaves:
16 32 64 128 256 512 1024 2048 4096 8192 16384 32768 Hz
I can’t hear much over 20 kHz in terms of pure tones, but calibrating for an extended high-frequency response tends to give better results in the audible band. And everybody - not just teenagers or dogs - can hear the extra octave (or 2, or 3) of bass.
Suffice to say, 11 octaves surrounding 20 Hz - 20 kHz is pushing the limits of our hearing system in terms of tonal range.
Dynamic range #
0 dB is the ‘noise floor’ of human hearing. Tinnitus and hearing loss will raise an individual’s perceptual noise floor, but in most situations the ‘room tone’ will be the biggest contributor to the noise floor, so I’m just going to skip over that, with a caveat:
With no input signal, audio equipment should not be audible from the listening position.
The dynamic ‘ceiling’ is the highest sound pressure level (SPL) that the speaker system can produce at the listening position.
To fully maximise dynamic range, the room must be made as quiet as possible, and the speakers as loud as possible. But our threshold of pain is between 100 and 120 dB, and environmental noise rarely drops below 30 dB. And we don’t tend to listen to music at these extreme levels.
Sound engineers like to make mixing decisions with their speakers set to produce 85 dB © at the mix position - which is pretty loud. In an extremely quiet studio, that’s about 60 dB above the noise floor. In your living room, only about 30 dB.
So, we really aren’t looking for the full 120 dB of dynamic range. We’d be doing great with 60 dB of measured dynamic range at the listening position.
Linearity #
Linearity describes a 1:1 correlation of input signal to output signal.
There are two aspects to linearity in terms of speaker systems.