On Fri, Feb 17, 2012 at 12:32:01PM -0500, gene heskett wrote: > [bolometers] > Either of those methods costs 500-5000 USD to accomplish.
The average house & garden multimeter is indeed completely useless for measuring anything audio. OTOH * There are quite good handheld audio RMS meters which don't cost a fortune (but they are in the higher price range). They use analog integrated circuits which can be quite accurate - at least for normal audio use. They are not laboratory standards of course. * Any pro-quality audio card, once calibrated against a known signal and combined with some simple software will make a near-perfect RMS meter *for the audio band* and as long as you don't drive it into clipping. > [cable impedance] > Why? The common two wire & foil shielded audio cable, used in broadcast > and studio facilities in miles per studio quantities, actually has an > impedance in the 60 ohm area! Feed it with a 600 ohm source and 300 feet > of cable later its rolled off like a Ma Bell telephone circuit. Your audio > DA's, to drive that, need to source terminate at 30 ohms per wire, from a > very low impedance amplifier. The concept of cable impedance makes sense only if the lenght becomes a non-trivial fraction of wavelength. For audio that means that for anything shorter than a few hundred meters it's only capacitance that matters. And yes you need hefty line drivers and low output impedance to push 20 kHz, +20 dBu on a long line. Which is one of the reasons why real pro quality analog audio remains expensive. Ciao, -- FA Vor uns liegt ein weites Tal, die Sonne scheint - ein Glitzerstrahl. _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
