Weak current College】 【determine mixer input gain a common method.

<br> This article from the practical and theoretical aspects of elaborated set mixer input gain the right way, with a detailed discussion of the sound source, microphone, mixer specification relate to each other. On radio and television fields of audio production staff with strong .guidance. <br> Keywords: sound mixer input gain, dynamic allowance, microphone sensitivity, maximum output level in the audio production process, a mixer input gain adjustment is correct or not, a direct impact on the quality of audio works. It should be .noted that a good grasp of the mixing console signal input, the first hurdle is to obtain good acoustics crucial step. Mixer input gain determines are common to both of the following methods: <br> 1. test method <br> This method is suitable .for the sound pressure level, microphone technique, sound mixer input gain and dynamic margin ignorant of adjustments. <br> First of all to adjust microphone and sound sources of distance, and then a mixer microphone amplifier (words) in the input gain knob counterclockwise .gateway to a minimum, will enter the channel mixer, listening channel, total output channel of sliding attenuator placed gain 0dB scale of 1 to the sound source for maximum sound pressure level, slowly clockwise open words input gain knob, the observation of this input channel .and total output channel meter to indicate normal is not overloaded, then get the volume range, then the input gain is the correct input gain sound mixer. Or you can take the following method: first turn off the input channel, listening channel, total output .channel of sliding attenuator and counterclockwise rotation small words input gain, then press the "PRE" button, in the accompanying sound source for maximum sound pressure level opening words input gain knob, through observation of input and output volume table method determines the sound mixer input .gain. <br> 2. calculation method <br> This method is based on the source of the sound pressure level, microphone and sound mixer specifications, the computed results, for any sound source, microphone and sound mixer are both universal and adaptability. .<br> Before the introduction of the calculation method, it is necessary to look at the following problems. <br> 2.1 microphone specifications <br> Broadcast microphone more common technical indicators, relative to the sound source and a mixer, the most important is .the following: maximum input sound pressure level, sensitivity, maximum output level. The former is the microphone can afford 0.5% total harmonic distortion of the maximum sound pressure level of the measure, its relationship with the sound pressure is defined as: 0dBSPL = 2 .× 10-5 Pa. As a professional microphone maximum input sound pressure level is generally done more, so long as it is the distance between the source and placed properly, would not have been audible distortion. So let's talk more directly influence the sound mixer .input gain for the latter two indicators: <br> 1) sensitivity <br> Is the microphone on the unit of sound pressure excitation, the output voltage and input sound pressure ratio (mV / Pa). To the same circuit-level linking, .sensitivity also has its own DB. Early DB expressed as dBm and dBV: <br> 0dBm = 1mW/Pa, that is, under the input sound pressure 1Pa to 600 Ω load brings 1mW power output defined as 0dB; <br> 0dBV = .1 V / μ bar, means that 1 μ bar input sound pressure arising under voltage output to 1V 0dB. <br> And now for the DB said: dBu <br> 0dBu = 0.775V/Pa, that is, define 1Pa input sound .pressure under microphone voltage output for 0.775V 0dB. (This will put the microphone sound pressure - voltage level measurement after the conversion, the circuit common 0dBu = 0.775V this reference unit). <br> Obviously, no matter how sensitivity that we .can convert it to dBu. The premise is to add their input into this unit Pa. <br> For example NEUMANNU89 microphone sensitivity is 8mV/Pa, directly from 20lg [(0.008V/Pa) / (0 775V/Pa)], .its sensitivity is about-40dBu. <br> AKGC414 microphone sensitivity to-60dBV, by 0dBV = 1 V / μ bar = 10V/Pa, first find the sound pressure-1Pa 60dBV output voltage X: 20lg [(XV / Pa) / .(10V/Pa)] =- 60 draw: X = 0.01 (V), that is, its sensitivity to 10mV/Pa; then-20lg [(0.01V/Pa) / (0.775V/Pa], they can have their .sensitivity is about-37dBu. <br> 2), maximum output level <br> Microphone in maximum input sound pressure level of the output level is the maximum output level. As maximum input sound pressure level qualified with the microphone and the distance between the .sound source relationship, maximum output level directly determines the sound mixer, then put the input gain, or enter a work level. For a given handset, known for its sensitivity and the high pressure level, you can calculate its maximum output level. <br .> We have a case study in U89 microphone: its sensitivity to 8mV/Pa, maximum input sound pressure level for 134dBSPL (10dB input attenuation stalls). We will input sound pressure level into sound pressure, and the sensitivity to its maximum output level: .because 0dBSPL = 2 × 10-5 Pa, maximum input sound pressure X by 134 = 20lg X (Pa) / 2 × 10-5 (Pa), concluded that: X = 100 (Pa); sensitivity 8mV/Pa, at maximum .output 100Pa as 800mV into output level: 20lg [(0.8V/Pa) / (0.775V/Pa)] about 0dBu. This is U89 microphone theoretical maximum output level. In fact, as a result of normal use we mostly do not select .a 10dB attenuator stalls (to reduce the input noise), so long as the receiver of a substantial distance, before U89 maximum sound pressure level is less than its normal stall under 124dBSPL, therefore its maximum output level is generally much lower than 0dBu. < .br> 2.2 mixer input gain, OK <br> From a technical perspective, the gain is a mixer input to its maximum of signal level does not exceed the manufacturers set maximum dynamic allowance limit to provisions (of course the actual input gain have to be .considered works of art needs to be determined, do not go into here). Here, the maximum dynamic allowance refers to the total harmonic distortion in the maximum levels and the section between 0dBu level range. <br> So, as long as the microphone .this end see sound source possible maximum sound pressure level and the sensitivity of the microphone, you can calculate the corresponding maximum output level; this level and mixer difference dynamic allowance limit is a mixer input level ie words should have the input gain, gain of signal .level is mixing console's work level. <br> Us to the sound source is small, the microphone is U89, mixer is a case study of AMEKRemBandt described: If the distance between the microphone 50cm Office sound source maximum sound pressure level is 112dBSPL (peak ., A-weighted), the receiver can withstand the maximum input sound pressure level is 124dB, sensitivity is 8mV/Pa; then, type: 112dBSPL = 20lg X (Pa) / 2 X 10-5 (Pa), the sound pressure level .can 112dB equivalent 8Pa sound pressure, it may have 8Pa × 8mV/Pa = 64mV voltage output, ie 20lg [(0.064V/Pa) / (0.775V/Pa)] =- 22dBu level output. This level to join words gain is .70dB, words-level dynamic margin in total harmonic distortion is 0.017% when the mixer 12dBu after (the sound mixer line zoom-level dynamic allowance for 28dBu), distance + ceiling there 12dBu 34dB of allowance [+ 12dB-(-22dB) = .34dB], this is a mixer should have input gain. This will determine the level of the mixer's work. <br> Of course, the actual operation, the mixer words input gain adjustment is not only a purely technical problem, to a large extent ., also affected by the works of art requirements, therefore cannot generalize, dogma. <br> <br>.