Here are a few thoughts that might be useful...
In
analog systems, there is always a background noise level. When the signal (music) level is low, that background noise becomes a larger fraction of the overall output, so the signal to noise ratio drops. Generally speaking, each device in the chain adds its own background noise, so that it's usually best to have the input signals high enough to exceed that noise level. In practice, this means that most of your gain should come from the first stages in your signal chain (e.g., your preamp).
If the gain is made too high, however, you run the risk of clipping and distortion. [Although it isn't typical, and is usually a bad idea, in some cases amplifier gain is controlled by modulating the negative feedback. This has the interesting side effect that distortion can increase systematically as gain is increased. I emphasize that very few circuits use this approach, however.]
Digital systems have a somewhat uglier set of relationships. When sound level is controlled numerically (i.e., the binary numbers representing the music data are scaled by multiplication), reducing the gain adds digitization noise from loss in resolution. For example, if you are sending music from your computer, tablet, or phone, to an amplifier system via a network, lowering the volume at the source (computer or handheld) ALWAYS results in increased digitization noise and distortion. Therefore, for the best sound, the level from your digital source should be set as high as possible, and then adjusted on your preamp using analog controls.
A well-designed preamp
can use a digital control to adjust analog gain. In such systems, the digital portion might change the electrical resistance in a portion of the circuit, effectively becoming an analog volume knob. This is the best situation for signal to noise ratio in digital systems.
| | If you want to hear this for yourself, try this experiment: If you have a digital connection (such as WiFi, USB, or ethernet) from a phone, computer, or tablet to your amp and speakers...
- Turn the volume all the way down on your amp/speaker system.
- Turn the volume all the way down on your digital phone, tablet, or computer, then increase the volume by one click.
- Start playing some music and increase the amp/speaker volume until its loud enough to listen. If it still doesn't get loud enough, increase the volume on your digital device until you can hear the music well.
What you should hear, is an example of digitization noise and distortion (quantization) |
Power Amps: The level controls on power amps
do not control the total output power that they can deliver. Instead, they are (almost always) attenuators that control the input levels.
tl;dr...
BOTTOM LINE(s) FOR BEST SNR and LOWEST DISTORTION
1. Front-end devices, including preamps, digital signal sources, microphone preamps should be adjusted to run at their highest output levels without clipping.
2. For devices between preamp and power amp, with the input sources set as above, adjust the gain to its maximum before clipping. Digital devices (DSP) should generally have only an output gain setting. If it is calibrated in dBm, you should set the DSP output between -6 and 0 dBm. This will ensure that there is plenty of headroom for peak music passages.
3. To set up the power amp level, adjust the input controls to play as loud as you ever expect to want to listen, then turn up the gain a little more (3 dB, or so, if the controls are calibrated) to give you a little room in case the source levels from your favorite recordings are a bit low.
