Tutorials: Just What is ‘SQ’?
- Thursday 15th April, 2010
Sound Quality, or "SQ" in audio entertainment terms, is a measure of the ability of a sound system to accurately convey a reproduction of a performance to the listener. A "Hi Fi" or high fidelity system would be considered to have good SQ. Sound systems with good SQ should transport you sonically to the actual performance of the music played. In the case of synthesised electronic music, sound quality will be the measure of how well the artist's music is represented by your audio system.
There are several broad aspects of Sound Quality which describe the way the sound is presented to the listener. Staging, Linearity, Dynamics and Ambience are broad aspects of Sound Quality which can be broken down further for better explanation. All these elements of SQ contribute to the total listening experience and are explained here to help us better understand the term "Sound Quality" and how it applies to our audio system, and our listening experience as a whole.
Staging, sometimes also called Imaging, describes the locations of musical instruments or the "Sound Stage" as it was recorded - such as if the guitar was on the left, bass on the right, drums in the centre (at the back), and a singer at the front of centre stage.
The above picture, "Jazz Band" from britannica.com is a fairly standard layout for many live jazz concerts. The locations of the musical instruments heard in a system with good SQ will be easily located in the sound stage.
Staging describes not only the location of performers, but also dimensions of the sound stage. Width, Height and Depth should appear to resemble the size of the original recording space, and define the boundaries of the sound stage. The trombone is on the far left side of the room, but how far from the centre, or from the side wall?
Stage Width is the distance from the furthest sound on the left of the sound stage to the far right. It may be a sound from off-stage, or right in the middle.
Stage Depth, as it sounds, is the distance from the closest to the furthest sounds. A vocalist may be close to the microphone with intimacy and closeness. However, on loud verses their voice echoes and reverberates from the back corners of the room. The drums are usually located behind the musicians and should sound as such. Some recordings are designed to clearly reveal the Stage Depth by placing instruments unusually far back, or close to the back wall of a room, and contrasting this to other sounds nearer to the microphone.
Stage Height can be elusive to all but the best SQ sound systems. You should be able to tell if the guitarist is standing or sitting. In a well recorded acoustic guitar and singing performance, the lead vocalist appears to be near the microphone with the guitar, whilst a backing singer stands nearby. Good Stage Height in a system will make it obvious if performers are standing or sitting, and whether their instruments are large or small in comparison.
Another aspect of staging is Focus. In our virtual sound stage, the cornet should sound like a smallish instrument with a narrow opening at the end. In a system with poor focus, the sound tends to smear and seem to be 'just somewhere in the middle'. Focus will let you hear how far apart the instruments are, what size, and whether one is in front of the other. A system with excellent focus will allow you to hear minute details in the recording which would otherwise be 'masked' by the blurred focus.
When listening to the complexity of an orchestral recording on your system, Staging will mean you are able to pick out where the 1st and 2nd violins are located within the recording. Or the tuba or kettle drums. Good staging means that you know they're in the right place in the sound stage and that the size of the room is accurately portrayed.
Linearity is a measure of the "frequency response" of an audio system. As a worst-case, when the low bass sounds are too loud or the crash of cymbals is too quiet, then linearity is almost certainly very poor. The frequency range considered ideal for an SQ system is 20Hz to 20kHz. Most musical instruments including the human voice fit within this range, as detailed in this chart of instruments:
If any of these frequency ranges are too loud or too quiet, the sound is said to be 'non-linear'. It will sound uneven, and you may not be getting all the information that is in the recording. Like a photograph where some of the red colour has faded a bit, you don't know what the colours are supposed to be; missing some of the mid-range frequencies (of a guitar solo, for instance) is still recognisable as a guitar solo, but it will be hard to tell what the real guitar sound should be. The fat plucked bass guitar sound on your audio system should not be thin, it should be fat. Nor should the strings sound as if they are too thick. A sound system with good linearity will reproduce the sounds of the instruments as they were recorded.
Linearity in SQ terms is broken down into sections called Bands:
Sub Bass is the lowest frequency band which starts below 20Hz and up to 80Hz. In the Sub Bass section are the lowest musical notes of Pipe Organ, Contra Bassoon and Piano. The powerful thud or boom of a bass drum and the 'fatness' of the bass guitar are also reproduced in the Sub Bass frequencies. Too much Sub Bass will make the sound boomy, too little will lose 'feeling' and realism in full-range recordings, such as Tchaikovsky's 1812 Overture.
Mid Bass, 80Hz to 300Hz, carries the main dynamics and impact of the lower frequency sounds. The growly resonance of male (and some female) vocals, the tactile kick or strike of the drums, and the main notes of the bass guitar are all in the Mid Bass frequencies. This is where we hear the 'body' of string and percussion instruments. Too much mid bass will 'muddy' the sound, while not enough will sound thin and possibly unengaging.
Mid Range is the widest range of frequencies, from 300Hz to 3kHz. Most of the sound we hear from day to day is in this range, and this is where our hearing is most sensitive. The intelligibility of vocals, the fine details of percussion sounds, the main voice and breath of instruments is heard in the Mid Range. Too much Mid Range will sound shouty - like a megaphone or other horn. Too little and the sound may be muffled or lost in the mix. It is often overlooked, but Mid Range frequencies are extremely important for location of lower frequency sounds in the sound stage, and can be the difference between merely 'good' bass sound, and 'excellent' bass sound.
High frequencies from 3kHz to 20kHz give us good location cues for mid range and high notes, as well as sparkle and openness in the sound. The crash and ringing of cymbals, the tinkle of bells and the hard-sounding edge of a whistle are high frequencies. Sibilance (hissing) and scratchy sounds are in the high frequencies also, and if over-emphasised will be fatiguing to listen to for long periods. Conversely, not enough high frequency sound will seem lifeless and soft, and many location cues may be lost.
Arguably though, the most important aspect of linearity is Phase. The phase of the sound describes how different frequencies arrive at our ears at the same time; for instance, if the low frequency beat of a drum reaches our ears before the whack of the skin, the drum will sound unusually thick, or woolly. If the different notes of the violin reach our ears at different times, the distance of the violin from the microphone will be indistinct, and the sound will be smeared in stage depth and time. When the phase of an SQ system is correct, the instruments will be more realistic, and the sound stage will take on a true third dimension in the mind's eye.
Dynamics in SQ terms describes the limits of a system to reproduce the loudest and the quietest sounds with realistic sound levels. It is thought that the minimum required dynamic range for realistic reproduction of live music is 90dB. Dynamics include the subtleties of sound, loud or soft, and allow the SQ system to accurately portray the smallest and largest details. From the soothing effect of stroking a drum with a light brush to striking the drum with a hard stick that makes you wince with each beat; a truly dynamic SQ system will reveal every detail in a quiet passage, just as it will not overload or distort with loud music.
Micro Dynamics are the finest nuances in how an instrument may be played. You may be able to hear if the cellist has sticky fingers, or if the pianist forgot to trim her fingernails this week. Micro dynamics are lost with all but the lowest noise levels, whether externally from the sound system, or from within the circuits themselves. Micro Dynamics are usually lost at -30dB lower than the quietest of the main program level.
Macro Dynamics will pound you in the chest and wake you up (because you were dozing during the quiet part) with loud, realistic sounds. Snare drums, timpani drums, breaking glass and plucked bass guitar strings use Macro Dynamics to be realistically reproduced in an SQ system. The biggest system requirement for Macro Dynamics is having a strong power supply and plenty of power on-tap in the amplifiers so that the system can reproduce the biggest peaks in the music. Macro Dynamics can be easily up to +20dB above the main program level.
Based on our earlier requirement of 90dB dynamic range, this leaves our main program level with a range of -40dB to +0dB. This may seem like a very narrow range, but keep in mind that most modern music has a dynamic range of less than 20dB, in some cases the music is compressed such that it only has 10dB of dynamic range - YUCK!. This high compression is fine for low-quality music reproduction in noisy environments, but not for realistic reproduction of our well-recorded music. The small dynamic requirements of modern music all of a sudden make our requirement for 90dB dynamic range seem excessive. This is not the case however. Below is a brief list of sound levels for various day-to-day sounds. Keep in mind that realism in a sound system depends on being able to make these sounds at life-like levels.
Our SQ system reference of +0dB is equivalent to 100dB of sound level in normal day-to-day sound levels.
The final and most immersive aspect of SQ is Ambience. When you listen to a great SQ system, you will get the feeling that you are a part of the performance. Ambience is the sense of space 'around' the sounds within the recording. You should be able to hear the echoes from the back of a hall with long reverberation. Ambient sounds within the recording such as the end of an instrument's solo that trails off into silence, or the general feeling that you can sense the performer's surroundings; this is what makes Ambience a real experience, rather than just listening to the music.
Now that we know what SQ is all about, how can we hear it? One good way is to find some quiet time when you won't be interrupted. Sit down in front of your system at home, or in the car if that's where your system is installed. Pick an album which you like, and have it play somewhat quietly, say at normal conversation level. Take note of the sound of each of the instruments and the voices. You may begin to 'see' straight away where the sound stage is, or you may get a sense of the space around the performers. Generally speaking, the best recordings for highlighting the strengths of a SQ system are acoustic recordings of Jazz, Classical or Blues. Some experimentation may be required to find which of your albums are well-recorded. MP3 music should not normally be considered acceptable for SQ listening, as the encoding process destroys much of the musical information required to hear the effects described in this article. In the meantime, happy listening.
