Understanding Harmonic

Part 01The question behind Harmonic

Before we talk about the slider at the top of the screen, ask one simple question: what makes two lossless recordings of the same performance sound different?

Not the level, bit depth or sample rate. What changes is the distribution of tiny harmonics (integer multiples of the fundamental) added to the signal. Every real DAC adds some, heard as “warmth”, “edge”, “presence”, “air”. Harmonic sets how much of each, 2nd to 10th: nine bands, applied in the FPGA before the discrete switching array driving the headphones.

Added at the bit-stream layer, the effect is lossless with respect to the source file, which is never modified on your SD card. With Harmonic off, even for one track, the signal is mathematically identical to a pure Δ-Σ reconstruction of the original PCM. Since V12 the switch is instant and survives reboots; switching back on restores your profile.

Part 02Why DX340 can do this

Most digital audio players ship with a fixed DAC chip — Sabre, AKM, Cirrus. That chip's harmonic character was decided at the silicon factory and cannot be altered.

DX340 is different. iBasso replaced the DAC chip with an FPGA and a discrete switching array of 512 pulse-width elements, in four groups forming L+, L−, R+, R− directly: true balanced output at the silicon, no analogue differential stage. The programmable FPGA can voice this hardware as a warm tube amp, a neutral reference DAC or anything between; Harmonic is its user-facing surface.

Part 03What “Band 1” really is

The app labels the nine sliders as B1 through B9. This is the hardware bank index and we display it honestly. Musically, our working model — from listening and measurement, not an iBasso specification — is that you are adjusting:

There is no “1st harmonic” because the 1st harmonic is the fundamental itself — and you cannot boost the fundamental, that would just be a volume knob. Real harmonic control starts at the 2nd.

The table assumes a 1 kHz test tone; overtones move with the note. On an A4 violin (440 Hz) the 2nd harmonic is 880 Hz, the 3rd 1 320 Hz. Harmonic is not a fixed-frequency equaliser: it says “boost the 2× overtone of every note”, not “boost 2 kHz”. Bass notes get low-frequency reinforcement, high vocals high-frequency, so it sounds natural where a parametric EQ centred at 2 kHz would sound artificial.

Part 04Even vs odd — the single most important thing to know

Centuries of acoustic instrument design — and half a century of audio electronics design — have settled on one rule that is as close to a law as this field has:

Even harmonics (2nd, 4th, 6th, 8th, 10th) make a sound warmer, rounder, sweeter.
Odd harmonics (3rd, 5th, 7th, 9th) make a sound harder, edgier, more cutting.

Physically, the 2nd and 4th harmonics lie exactly one and two octaves above their note: musically they are the same note, just higher, so the ear hears reinforcement, not dissonance. Odd harmonics land on other notes: the 3rd an octave-plus-a-fifth above, the 5th two octaves plus a major third, the 7th a flat minor seventh the brain reads as tension. Too much odd content sounds sibilant, harsh, fatiguing over time.

This is why tube amps are prized for warmth. Tubes, when overdriven slightly, generate almost exclusively even harmonics. This is also why cheap solid-state amplifiers are often called “clinical” or “sterile” — they generate slightly more odd harmonics than even ones, and the ear hears it as edge.

For a custom Harmonic profile, remember one rule: for warmth, lean on B1 / B3 / B5 / B7 / B9 (even harmonics); for clarity and bite, B2 / B4 / B6 / B8 (odd harmonics). Never max everything out. A good profile is a few deliberate choices: usually two or three bands pushed a little, the rest at zero.