ruffrecords said:
I see lots of questions about signal and noise levels when people interface external mic pres with a DAW. The issue is usually they have no idea of how real world signal levels translate into dBFS readings in their DAW and the interface and DAW manufacturers don't make this any easier. So I wondered if there is a project for a DIY 1KHx 0dBu sine wave generator.? Fits in your pocket and powered by a PP3 or similar. You plug it into you interface and you instantly know how many dBFS equals 0dBu. Or maybe this exists aleady?
Cheers
Ian
First I had to figure out what a PP3 is (9v battery).
More than enough PS voltage to make a conventional technology analog low distortion, amplitude stabilized, 0dBu audio signal (0.775Vac). In addition I would be tempted to add a low battery voltage indicator to increase trust in the signal integrity, since weak batteries could degrade output.
I try to avoid hardware products that can be covered with a smartphone app but modern smart phones seem less serious about providing audio output signals.
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I did a quick survey of VOM /multimeters to see if any provide a reference audio output, easy enough to include, the closest I found was one that provided a 20ma current loop output.
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For today's TMI, over the decades I scratched out a lot of discrete design ideas after beer o'clock to make a simple multi-capability pocket audio troubleshooting tool. This would work from a single AA, or maybe AAA cell for compact size.
The basic concept is a simple astable multivibrator. When the probe leads are unloaded (open circuit) the circuit stops oscillating to conserve battery life. The frequency of oscillation is determined by the load resistance. In an ideal world for audio troubleshooting this would cover impedances between 4/8 ohm for speakers, 150-600 ohm for mics, 2k for mic preamp inputs, and 10k for line level inputs.
The output would basically be a square wave and the voltage would scale so the highest output level would occur for line inputs (10k), and significantly lower into mic inputs (2k).
The square wave would crudely excite loudspeakers with audible sound.
This is not for lining up 0VU levels, but crude troubleshooting to find open wire lead connections, and faulty signal paths.
Needless to say I never progressed to melting solder, and it seems like wishful thinking to cover loudspeaker impedances and line inputs without at least a range switch.
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Now after going over to the dark side I need to see about microprocessors that will run from 1V battery power.
JR
@Ian wrt PIC, they make many cheap ones with 8 bit a/d built in. I don't remember finding real audio DACs built in until the more serious DSPics (16b), but I haven't looked lately... I made lots of serviceable enough sine waves for my drum tuners using cheap PIC PWM outputs (smoothed by LPF). I need to see what they sell now that will run down to 1V battery.... actually never mind, I pass.