Today I started performing basic THD+N and SNR tests for the LA610′s.

First, let’s talk about the test methods we’re using. I’ll be using the AES standard for testing mic preamps, which states that the preamp be tested at maximum gain, with an output of +4dBU. I chose to use a 1kHz signal with a -40dBV amplitude. I set the LA610′s 5 position “Gain” switch to +10, and its “Level” knob to 10. Mic input impedance switch was set to 2k. I put the compressor in “bypass” mode (which doesn’t bypass the T4UA but disconnects the level detector). The output “Gain” knob was set to give a +4dBU output into a 600 ohm load (yes, that’s technically +4dBm).

Below is a Bode plot of the measured response under this test:

I took about 20 test measurements for THD+N, SNR, and THD for the LA 610′s because I wanted to ensure that the results I got could be duplicated, and chose a plot that showed an “average” response. I placed several markers on the test screen for reference, so its possible to see what the relative dB of individual harmonic distortion components were in relation to the fundamental tone, as well as how far the harmonics extend within the measurement band.

It’s important to note that the SNR figure seen on the plot is the measurement under this test isn’t considered an “official” published SNR figure because it doesn’t follow test standards to determine SNR. But it does give us some indication of how the LA610 would perform in an SNR test. If you want to know more about how to calculate an “official” SNR figure (or any of the other tests I’m performing), Rane’s Audio Specifications page is an excellent resource.