Mis à jour le 31 March 2021.
When buying a hi-fi amplifier , a hi-fi preamp , a CD player , a Turntable , a digital audio player or a headphone amp , many parameters can guide us in our choices: the amplification power and the connections, the type of discs supported and the integrated DAC or the type of drive and the cartridge supplied.
Although often neglected, the signal-to-noise ratio is nevertheless an important feature for gauging the quality of a hi-fi element.
What is the signal-to-noise ratio?
Any electronic audio device (amplifier, preamp, CD player, turntable, etc.) generates more or less intereference signals and background noise which are affecting the sound signal. It is the very functioning of its components (capacitors, transistors, resistors, etc.) that generates this noise.
The signal-to-noise ratio (SNR) is expressed in decibels (dB) and indicates the level difference measured between the background noise generated by the circuits / components of a device (hiss when no signal passes through it) and the signal at its nominal level (defined at +4 dBu on analog devices, which corresponds to the “0” level of the VU meters of amplifiers, for example).
The higher the signal-to-noise ratio of a device, the lower its background noise, in other words the more “silent” its operation. Quieter operation makes more subtle sounds more audible.
It is generally considered that a good signal to noise ratio is 60 dB or more for a phono turntable, 90 dB or more for an amplifier or CD player, 100 dB or more for a preamp.
What are the different sources causing noise?
What is component noise, or internal background noise?
Without going into overly technical explanations, it should be known that there are different types of noise in an electronic system, which are linked to the physical characteristics of the electronics as well as to their manufacturing quality. It is this noise level that is expressed by the signal-to-noise ratio mentioned in the technical specs of the various hi-fi devices.
Fundamental noise is noise linked to the intrinsic physical properties of components which generate statistical fluctuations in current and voltage. These fluctuations and the noise they induce occur randomly and cannot be avoided. The two main fundamental noises are Johnson–Nyquist noise (thermal resistance noise also known as Johnson noise) and shot noise, also called quantum noise. Johnson noise is generated by the disordered movements of electrons in matter, movements that are accentuated as the temperature rises. Hence the importance of cooling certain sensitive components by means of aluminum radiators (finned), for example.
So-called “technological” noise is due to technological imperfections in the components. There are mainly two types of technological noise that mainly affect low frequencies: burst noise and flicker noise. Technological noise is directly linked to the manufacturing quality of the components. This is how we distinguish low noise audiophile components, which are optimized, from “standard” components.
Finally, Zener noise and Avalanche noise are a combination of fundamental noise and technological noise. They originate from inevitable statistical fluctuations, but their magnitude is linked to the technology used in the components concerned. Optimized components can thus reduce these noises significantly, without however being able to eliminate them completely.
About external noise
In addition to the background noises that can be generated by the internal components of an amplifier, a CD player or any other hi-fi or home theater component, there is a risk of noises generated by external sources. We generally speak of electromagnetic interference (EMI) or radio-frequency interference (RFI).
These disturbances can be generated by switching on a lighting or an electrical device, by a poorly or uninsulated power supply or by a powerful electric current which circulates near sensitive components. The sudden flow of current in domestic electrical circuits when a lighting or appliance is switched on (refrigerator and freezer motor, washing machine resistance, electric oven, electric heater, building lift, etc.) can cause an electromagnetic wave and induce currents and voltages in the circuit of the audio device. It can also generate a fluctuation in the electrical network which propagates in the power supply of the hi-fi device and influences the audio circuits.
What is the impact of noise when listening to music?
The noise generated by the electronic components takes the form of a more or less noticeable hum. The lower the signal-to-noise ratio, the more important and audible this hum is, in particular during quieter passages or silences. This is why we sometimes talk about the quality of the silences of an amp. This is another way of talking about the signal-to-noise ratio. If, an amplifier does not generate audible hiss through speakers or headphones when running and with no signal going through it, then its signal-to-noise ratio is satisfactory. Note that the hum will be more audible with high sensitivity floorstanding speakers,bookshelf speakers and hi-fi headphones high sensitivity than on low sensitivity speakers or headphones.
Admittedly, the hum generated by a device with a low signal-to-noise ratio can be covered by music when the volume is turned up. But its impact is far from negligible. First of all, because it makes listening at low volume less pleasant: a hum similar to white noise in the background is never appreciable. Secondly, because it masks the quietest signals and therefore loses certain information. Conversely, electronics with a high signal-to-noise ratio reveal much more micro details of the recording, thus enriching the listening experience.
How to improve the signal-to-noise ratio of your system?
The first step in optimizing the signal-to-noise ratio of your system is to choose electronics whose design is optimized to reduce noise sources (values, number and quality of components, design of circuits, anti-interference shielding, isolation of sensitive components…).
It is also possible to take care of the supply of the various elements of the system to prevent them from being subjected to electrical pollution of the domestic network. To do this, you can dedicate a line to your audio-video system on the electrical panel by pulling one or more large-section electrical cables to the listening room. You can also use wall outlets, multiple sockets (filtered or not) and high-qualitypower cables with pure copper contacts, large wire gauge and effective shielding. One can also resort to power conditioners (mains current filtering devices) which eliminate interference and protect devices against voltage spikes.
The analog cabling between the devices, in particular the RCA link cables, must also be carried out with stereo RCA cables that protect signals from external interference with effective shielding.
All these precautions and arrangements make it possible to significantly reduce noise, whether it is of internal or external origin.
What about the background noise in the room?
Do you live in a noisy neighborhood or near a busy road? Does your kitchen dieectly opens into the living room, resulting refrigerator noise interfering with music? Is your air conditioner noisy?
In this case, the background noise in your listening room is undoubtedly more problematic than that generated by your electronics, resulting in a very unfavorable signal-to-noise ratio for your audio system.
How to fix it? By systematically hunting down noises to reduce or even eliminate them.
Several solutions exist, starting with installing your audio system in the quietest room in the home and the most distant from any source of parasitic noise.
You can also proceed with the sound insulation of your room, for example by investing in double glazing and in an insulated or even padded door. Putting insulation or heavy upholstery fabric on the walls can help matters as well.
If the devices that generate noise and mask the quietest sounds of music cannot be moved (refrigerator, freezer, VMC, air conditioning, etc.), then consider turning them off for the duration of your listening session or during the movie. Listening with headphones is also a very good solution in a noisy environment, in particular with closed-back hi-fi headphones.
Choose a hi-fi amplifier , a hi-fi preamp , a CD player , a Turntable , a digital audio player , a headphone amplifier or any other electronics that has a high signal-to-noise ratio is the inssurance of enjoying music without hum or background noise and being able to hear a multitude of quieter sounds (what is called micro information). The sound is then richer, more precise and more nuanced.
However, even with such electronics, attention must be paid to other sources of noise such as noise and electromagnetic interference. These can be addressed or even eliminated by using shielded RCA cables and power cables, filtered power strips and / or power conditioners.
As for the background noise in the listening room, it can be more difficult to eliminate, especially when you live in a noisy area. Some home improvement work may then be necessary to improve things (soundproof windows, sound insulation). Noisy devices can be temporarily disconnected so as not to disturb the listening session.