Sound Fidelity vs. “Pleasant” Degradation: How to Truly Assess Sound Quality?#
Introduction#
“High fidelity” means reproducing the source as faithfully as possible. The paradox is that some kinds of degradation can be pleasing to the ear—hence the popularity of reel-to-reel tape machines, tube-and-transformer gear, and vinyl records. Preferences are subjective and can’t be captured by a single number. What we can do is objectively describe what a given device does to the sound. This article brings order to the topic: instead of colorful but ambiguous prose, it presents measurable categories that fully define the fidelity of audio equipment.
Why can “degradation” be pleasing?#
Certain nonlinearities and bandwidth limits create artifacts the brain interprets as warmth, intimacy, or “density” of tone. Examples:
Tape saturation: compression of peaks and addition of higher-order harmonics.
Tubes and transformers: predominance of even-order harmonics, gentler clipping.
Vinyl: specific tracing distortion, noise, and bandwidth limitations.
Whether these distortions have a positive or negative impact depends largely on the program material—and results vary.
The problem with poetic reviews#
Audio magazines often speak of a “sparkling top end,” a “wide soundstage,” or “air hanging in the space.” Such language can be evocative but isn’t objectively verifiable—everyone interprets these adjectives differently. If we want to compare devices sensibly, we need parameters that can be:
measured,
correlated with perception,
reproduced under the same conditions.
The Four Pillars of Audio Fidelity#
Four categories are enough to describe everything that affects the fidelity of an audio chain: noise, frequency response, distortion, and time errors. Each contains subsets, but together they form a complete picture.
1. Noise
All unwanted signals added to the audio.
Noise level (SNR, EIN): how loud the noise is relative to the signal.
Pink/white noise, hum, mains buzz: the spectral character of the noise.
Modulated noise: noise that changes with the signal (particularly troublesome perceptually).
Perception: higher noise masks details and reverb tails; at low listening levels it reduces intelligibility.
2. Frequency Response
How a device boosts or attenuates particular bands.
Flatness: deviations in dB as a function of frequency.
Filters and tone-shaping: intentional changes (EQ, RIAA equalization).
Load interaction: e.g., headphones with different impedances.
Perception: low-end boost reads as “fullness,” low-mid lift as “warmth,” treble lift as “brightness/clarity.” Uneven response most often explains “dark/bright” descriptions.
3. Distortion (Nonlinear and Linear)
How the device adds content that wasn’t in the input.
THD/THD+N: total harmonic distortion (tubes often add even-order harmonics perceived as “musical”).
IMD: intermodulation distortion (typically more audible and unpleasant).
Clipping/limiting: behavior when overdriven (hard vs. soft).
Linear distortion: e.g., response ripples from transformers, enclosures, resonances.
Perception: small, “soft” distortions can impart “density” and apparent loudness; IMD usually degrades clarity.
4. Time Errors
Everything that happens in the time and phase domain.
Jitter (digital): instability of sampling instants, affecting microdynamics and transient “sharpness.”
Wow & flutter (analog): slow and fast transport-speed variations.
Phase and group delay: arrival time of frequency components; crucial for stereo imaging and transient coherence.
Reflections/room: outside the device, yet crucial in shaping the temporal envelope.
Perception: time errors blur the soundstage, attacks, and source localization—even with a “flat” response.
How to translate this into listening practice?#
Set your goal. For recording classical/jazz or for mastering, we usually minimize noise, distortion, and response unevenness. For rock/pop/lo-fi we may intentionally introduce “color.”
Measure and listen. Measurement tells you what and how much; listening tells you whether you like it. Either one alone can be misleading.
Control levels. Compare at matched loudness (level-matching). Louder almost always seems “better.”
Test transients and tails. Check attack (snare, piano), decay (reverb, strings), and readability in dense mixes.
Think about the whole chain. Source → conversion → processing → amplification → transducer → room. Every link changes the result.
What about poetic language in reviews?#
Metaphors can help communicate impressions, but they shouldn’t replace parameters. If a review mentions “springy bass” or “air up top,” ask:
What do the response and distortion measurements look like?
Was the listening level-matched?
What were the room conditions and the load (e.g., specific headphones/speakers)?
Without concrete data, such colorful descriptions say little beyond conveying a certain emotion to the reader.
Summary#
Audio fidelity can be described directly and completely by four categories: noise, frequency response, distortion, and time errors. Everything else—“air,” “creamy mids,” “crystalline highs”—is an interpretation of the same phenomena, merely clothed in poetic language. There’s nothing wrong with liking “color.” What matters is knowing what creates that color and when it’s desirable. When the goal is documentary fidelity, we minimize departures. When the goal is “character,” we choose departures that suit the music and our taste. In my view, a discerning listener and seasoned engineer can move comfortably between both worlds.