Pro Audio Testing and Troubleshooting

Hi All

Is there any compendium/basic starter 101 of tests that need to be made to check functionality of builds? I will be testing a mixer, eq, compressor and some saturators...I was planning on using this plugin which is now able to test hardware:

https://ddmf.eu/plugindoctor/

It can do Linear Analysis, Harmonic analysis, Dynamics and it has a oscilloscope...I'm sure it is a massive subject so I'm looking for a starter and to go from there...I have some basic understanding on each of these areas but need to gain experience asap...

It often comes down to common sense beginning with visual inspection for quality of soldering. 

The basic VOM measurements requires understanding of circuitry and component behavior. (Trouble shooting circuits without a schematic is real fun).

Machine troubleshooting requires extensive programming and multiple test points. In production a "bed of nails" test probe fixture is sometimes used.

JR

thanks John

what is a good noise score for a analogue rack unit these days - below -70db? How about THD for a unit that should be clean?

Im also curious about the levels when harmonics/THD start to be come audible...

[edit] - I see the 'Meta-Meta' thread now with a lot to get my teeth into there...but of course any contribution welcome here also thanks

SWAN808 said:

what is a good noise score for a analogue rack unit these days - below -70db? How about THD for a unit that should be clean?

Im also curious about the levels when harmonics/THD start to be come audible...

Click to expand...

dB is a relative scale so there are different meanings of "noise score". The way I measure noise is I just put a tone in and adjust the level of the tone until it is just barely not clipping. The magnitude of that peak is a crude signal-to-noise ratio (SNR) type of measurement.

Doing that, better than 95dB SNR is pretty common I think. But it depends greatly on the circuit. If it's some passive LC filter like a Pultec HLF3C, it will be difficult to measure noise over what your USB audio interface can do just in loopback mode. If it has a lot of active circuitry, the noise added will be very measurable and hopefully not significant to the listener. Anything in the high 80's is respectable. Anything with large series impedances (like tube stuff) is going to be noisier.

As for distortion, a lot of very good recordings are pretty distorted. Many early recordings like Bo Diddley are heavily distorted and I think they sound great. I can only guess it's because they were trying to push as much signal onto the tape machine as possible. Probably sounds even better on a small transistor radio whilst sipping a Gin and tonic.

I played with the software on break. It was buggy and crashed but nice idea.

noise specks are only so much.  I'll give you an example, a certain company I know had mixers that when all channels were going would measure pretty poorly as far as noise.  The hiss was very obvious. Their solution was tell consumers that's the sound of analog.  it worked...

pucho812 said:

I played with the software on break. It was buggy and crashed but nice idea.

noise specks are only so much.  I'll give you an example, a certain company I know had mixers that when all channels were going would measure pretty poorly as far as noise.  The hiss was very obvious. Their solution was tell consumers that's the sound of analog.  it worked...

Click to expand...

thanks I will remember that one...I was planning on selling the sound of analogue but aim to try to keep it to the good bits...but if some of the other attributes creep in we will have to see