DP on the bench for tech use

[adeptusmajor]

Hello all,

I like to DIY most of my gear, and have used DP as a signal generator/meter/scope to calibrate some of my electronics builds.

This morning I ordered one of the new SCA B16 compressor kits, and looking over the build docs it looks like I need to have a means to measure THD+N to be able to get it to a minimum.

I am using DP6 still, does anybody know if there is an effective way to measure distortion and noise on the DAW? Sorry if I am overlooking something obvious, I am not quite a DP power user like many here are, plus, with electronics I am more of dabbler than an engineer.

Thanks for any help. Also, feel free to use this thread if anyone would like to post any other tips that would be helpful for DIYers using DP as a calibration tool.

[mrbillet]

You must mean you're using Cue Mix because DP doesn't provide much functionality on its own for this sort of testing. If I'm missing something please let me know because I'm always happy to find a new way to utilize DP.

Since you're into electro-acoustical testing and analysis have you checked out http://www.faberacoustical.com/" onclick="window.open(this.href);return false; ?

-ian

[adeptusmajor]

Thanks for the link. I believe I was looking at that app for the iphone when i was thinking about buying one, it would be very useful at work (I build and work on sound systems for a living).

What I need is a way to measure Total Harmonic Distortion and Noise in a signal, I can't tell if that program provides that (I have never had to measure THD+N before so I am unfamiliar with the process). The reason I am asking here is that the build manual for the SCA B16 states that "To adjust gain and distortion trim, you’ll need the ability to generate and measure audio test signals between –20dBu and +20dBu and THD+N down to 0.01%. Most DAWs can accomplish this task."

I figured that if most DAWs could, then DP definitely could (should). A simple tone/noise generator plugin, or maybe even more complex signal analysis would be a very welcome addition if you ask me.

I have used DP as a signal generator when calibrating equipment, more recently an SSL buss compressor clone. I just made a track and loaded a soundbite of a 1kHz -10dBu test tone. Using the meter bridge to monitor levels, I sent the tone out to the comp and then back in. I was able to calibrate the compression ratios and nominal gain of the unit very easily and pretty precisely this way.

Another easy trick, more to supplement acoustics than electronics, is to make a track of pink noise to tune your room. Just play the noise through your monitors and put a good flat mic at the listening position, then measure its frequency response. Put a MW EQ on your master out, and make adjustments to flatten what the mic is hearing. I wouldn't recommend doing anything too drastic before addressing the actual acoustics in your room, though. But it can be helpful for minor adjustments. Save the eq setting, you can now apply this to your master buss to help flatten the room while you are mixing, just don't forget to bypass/remove it before you bounce your track.

Anyway, if anyone else has any tips for measuring THD, I'm all ears.

Thanks

[adeptusmajor]

Ok, so someone asked the same question over at Seventh Circle Audio's forum. Tim recommended this standalone program http://romacsoftware.com/meterdefault.asp" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false; , which unfortunately appears to be windows only. But he also said you could use this plugin http://www.voxengo.com/product/span/" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false; which does have an audio units version. He said to simply run a low distortion sine wave through the comp and back, then use the FFT to visualize the harmonics, then adjust for minimum second- and third-order spikes. This isn't as precise as the first option, but seems like it should be pretty sufficient, so I guess I will go this route.

I am still open to other suggestions, though.

[DoctorOrbis]

Glad to see someone else using DP to automate their bench!

If you have a MOTU interface, CueMix FX has several analyzers available. I use the FFT analysis, oscilloscope and XY plot windows on an almost daily basis. I've used Faber's SignalScope in the field as a quick reference for mitigation of Larsen effect, and also for classroom demonstrations. I haven't had much luck getting it to play nice with external interfaces for precision measurements, though.

A good place to start if you want to understand THD+N are these white papers:

http://www.rane.com/pdf/ranenotes/Audio ... ations.pdf" onclick="window.open(this.href);return false;
http://www.analog.com/static/imported-f ... MT-003.pdf" onclick="window.open(this.href);return false;

For a hobby bench, CueMix FX and a MicroBook would be satisfactory, but for serious work I recommend an HD192.

-O-