A Couple Of Pointers To Help Understand The Signal-to-noise Ratio Of Recent Audio Amps

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To help you decide on an audio amplifier, I am going to clarify the expression "signal-to-noise ratio" which is regularly used in order to explain the performance of audio amplifiers.

When you have narrowed down your search by looking at a few basic criteria, including the level of output power, the size of the amp and the cost, you will still have quite a few products to choose from. Now it is time to look at a couple of the technical specs in more detail. Every amplifier is going to generate a certain level of hiss and hum. The signal-to-noise ratio will help compute the amount of noise produced by the amplifier.

Comparing the noise level of different amps may be done quite simply. Simply get together several models that you wish to compare and short circuit the inputs. Then put the amplifier volume to maximum and verify the level of static by listening to the loudspeaker. You will hear some amount of hissing and/or hum coming from the loudspeaker. This hiss is produced by the amp itself. Make certain that the gain of the amplifiers is set to the same level. Otherwise you will not be able to objectively evaluate the level of static between several amplifiers. The general rule is: the lower the level of static that you hear the better the noise performance.

Whilst looking at the amplifier spec sheet, you want to look for an amplifier with a large signal-to-noise ratio figure which suggests that the amplifier outputs a small level of hiss. Noise is created due to a number of reasons. One factor is that todays amps all employ components such as transistors and resistors. Those components are going to make some amount of hiss. The overall noise depends on how much noise every component produces. However, the position of those components is also important. Elements that are part of the amplifier input stage will generally contribute the majority of the noise.

Many todays power amps incorporate a power switching stage that switches at a frequency around 500 kHz. This switching frequency is also noise that is part of the amplified signal. Nonetheless, modern amp specs generally only consider the hiss between 20 Hz and 20 kHz.

Producers measure the signal-to-noise ratio by setting the amp such that the full output swing can be realized and by feeding a test signal to the amplifier that is typically 60 dB below the full scale of the amp. Then, the noise floor between 20 Hz and 20 kHz is measured and the ratio to the full-scale signal calculated. The noise signal at different frequencies is removed by a bandpass filter during this measurement.

Time and again you will discover the term "dBA" or "a-weighted" in your amplifier specification sheet. A weighting is a method of expressing the noise floor in a more subjective way. This method was developed with the knowledge that human hearing perceives noise at different frequencies differently. Human hearing is most responsive to signals around 1 kHz. Though, signals below 50 Hz and higher than 13 kHz are barely noticed. The A-weighted signal-to-noise ratio is generally larger than the unweighted ratio and is published in a lot of amplifier parameter sheets.

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You can get further information concerning digital amplifier models and t amps from Amphony's website.



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