Re: [LAD] Calibrating sound cards

On Mon, Apr 14, 2008 at 10:15:50PM +0100, James Courtier-Dutton wrote: It all depends on what kind of sound card you have - Consumer - Semi-pro - Pro The latter usually are calibrated, or have a calibrated gain setting. Some semi-pro's as well, e.g. my Terratec 88MT is matched rather precisely to my mixer when all levels are set at the +4dB setting and gains are set to 0dB. For consumer type cards there are no standards. The only thing you can do is connect it to a line/aux/cd input on your amp, play back a file with rather high levels and adjust both the card's mixer and your volume control until it's loud enough and sounds right. It also depends on what your card is connected to, what you use it for, and in particular if you have and/or want to use a volume control after the card, e.g. on the amplifier. For 'entertainment' this is perfectly OK, but in a studio setting you may want fixed levels, which means that gains are set so that the card will not overload on the highest peaks you ever want to reproduce, and volume is set in software. The typical result of doing this is that things like 'desktop sounds' will be much too loud. K3B almost blew out my speakers that way some years ago, which made me ban all KDE apps. What is OdB of Gain ? One side of an ADC/DAC is numbers, the other is a voltage. You can't compare apples to oranges... You could speak of a 'gain' if you have a defined 0dB voltage and compare it to maximum digital level, but it could be quite confusing... For audio the semi-pro level is -10dBu, and the pro level is +4dBu, with 0dBu being 775mV RMS. But these are 'normal program levels', and not the maximum. Normally these levels are set to correspond to around 12dB below the maximum digital level. Which means that a semi-pro card must be able to produce +2dBu (about 1 Volt RMS), and a pro card must be able to handle at least +16dBu (about 5 Volt RMS). Most AC voltmeters will give a completely wrong reading for typical audio frequencies. If you don't go too much above 100 Hz it will work. Ciao, -- FA Laboratorio di Acustica ed Elettroacustica Parma, Italia Lascia la spina, cogli la rosa.