A reader has asked about our use of sound signature in reviews for headphone, TV, soundbar, speakers, smartphones and other sound devices.

The answer is that a sound signature is a consistent way to describe a devices ability to reproduce sound. By comparison, a reviewer’s subjective comments from listening to their favourite soundtracks, although important, can vary wildly.

Why sound signature? Audio quality depends on so many things – the bit rate, sample rate, file format, and speaker construction. It also depends on the ability of the encoder to get the important bits right and the reviewer’s ears!

So, here is sound signature 101 and why we use it to rate sound devices

Frequency response – the human hearing range

Humans generally hear frequencies from 20Hz (bass) to 20kHz (treble). As you get older, the top end usually progressively falls off – it is not uncommon for the elderly to only be able to hear to as low as 3kHz. That is why hearing aids generally don’t boost volume, but boost lost frequency ranges.

But sound is a combination of hearing (tones and harmonics within the eardrum) and feeling (subjective impressions that depend on musical associations, your mood at the moment, and a bunch of oh-so-human indefinables). Oh, and throw in spatial variables like sound stage/separation (left/right, up/down, forward/behind), echo (the reflection off walls), speed of sound and timbre and you wonder how we can hear at all via two small ear canals.

Well, we have the world’s most powerful non-AI computer to post-process, fill in the gaps and make the most of whatever we hear.

That frequency response covers:

  • Deep Bass: 16/20-40Hz – which you can often feel more in your body that you hear in your ears
  • Midbass: 40-100Hz – if this is intact, you will be getting just about all the musically important bass
  • Upper Bass: 100 to 200Hz – most small sound devices, like portable Bluetooth speakers, start here
  • Mid: 200-4kHz– this is where the action is, it covers the human voice and is the area where our ears are most sensitive … even as we age.
  • Upper Treble: 4-10kHz – this defines the character of the sound. Its absence makes the sound dull.
  • Dog whistle – top octave: 10-20kHz – you can’t generally hear this, but you know if it is missing. Its presence improves the sense of direction in the sound and provides a feeling of “air”, a reality as though the music were really there, rather than merely reproduced.

Six sound signatures describe the natural state of the sound device.

Of course, you can have a combination of two or more, and many have equaliser and sound profile apps that can change the signature entirely often resulting in ‘frankensound’.

  1. Balanced: (bass boosted, mid recessed, treble boosted) also called V-shaped and the default on many devices – despised by audiophiles
  2. Bass: (bass boosted, mid/treble recessed) – for bass music but can sound boomy or muddy compared to warm and sweet
  3. Warm and Sweet (bass/mid boosted, treble recessed) – the nirvana for most music and movies
  4. Mid: (bass recessed, mid boosted, treble recessed) – for clear voice
  5. Bright Vocal (bass recessed, mid/treble boosted) – thought to be for vocal and string instruments, but actually makes them harsh
  6. Analytical: (bass/mid recessed; treble boosted) – crisp but can be overly harsh and not pleasant for most music
sound signature

We like to add a seventh – flat or neutral that neither adds nor subtracts from the native music, but this is rare – if it exists at all! Where possible, we test with the Equaliser (EQ) set to flat.

Flat means just that – and we seldom find it

So, if we say something is warm and sweet, you can count on it for good music.

Most sound devices are naturally mid-centric and use some form of psycho-acoustic trickery via ‘tuning’ the DAC (Digital Analogue Converter) or an EQ to boost specific frequency by several dB.

This can add a little bass, mid or treble, but it is not the speaker’s native signature. We often refer to this as ‘synthetic sound’ – it is not bad, but it is not entirely natural.

There is an excellent article here that delves into sound signature nuances although it uses slightly different terms.

Speaker types

Speakers range from small 4-6mm earphone transducers to monster cones. But we have yet to find a single speaker that can do it all – reproduce the full range of frequency response. Physics precludes this in loudspeakers, although some headphones and earphones can come closer to this ideal.

Some headphones can get great bass because they have an excellent over-the-ear seal – less air to push.

And this is because you need a larger speaker to push volumes of air for bass and a smaller, ‘shriller’ speaker for treble. So, in a decent soundbar or hi-fi system, you will have separate speakers (and amps) for bass (sub-woofer), mid, and treble (tweeters).

Then there’s the separate issue of surround sound. Typically

  • 1.0 – mono speaker and some use passive radiators to increase bass or reflectors to increase 180-360° sound
  • 2.0 – stereo speakers (L/R)
  • 2.1 – L/R and subwoofer
  • 5.1 – Front L/R, Centre (usually tuned for clear voice), rear L/R (often tuned for spatial effects instead of reproducing front sound – these are placed to the sides of and slightly behind the listening position) and a sub-woofer
  • 5.1.2 – As above plus L/R up-firing front speakers or ceiling speakers (Minimum for Dolby Atmos)
  • 5.1.4 – As above plus L/R rear up-firing rear speakers or rear ceiling speakers
  • 7.1.4 as per 5.1.4 but with L/R surround rear speakers
sound signature

The above cover the usual channels that a sound device can down-mix to. For example, if a 2.0 TV or soundbar claims Dolby Atmos compatibility, it means that it takes the 5/7.1.2/4 native signal and downmixes an approximation to the physical number of amps and speakers. Conversely, DTS:X up mixes (emulates) 1.0 or higher to the speakers capacity.