How to Amplify Voltage Reading From Audio Jack
Gain structure: input and output levels
This article describes input and output gain construction of audio devices.
Audio components are typically rated past their input sensitivity and/or maximum output voltage. This article explains how to match the output voltage of an sound device to the input voltage range of the next device in the signal concatenation, and how to adjust input sensitivity to accommodate a multifariousness of voltages from different source devices.
dB, dBu, dBV, dBFS, and dB-SPL
As a basis for the discussion it is important to sympathize the meaning of and differences between some of the common decibel units: dB, dBu, dBV, dBFS, and dB-SPL. Some background is provided as a prelude to the article.
A decibel (dB)is a logarithmic ratio of ii values. A decibel is a "dimensionless" value, meaning that it is simply a number, not a unit. While decibels are most commonly associated with sound signals, they don't necessarily accept to exist. When they are being used to describe audio point levels, they are often used to compare the amplitude of ii audio signals. If those two signals are the same amplitude, so they are said to be 0dB apart. If one signal is twice the amplitude of another signal, then it is 6dB higher. If someone tells you lot to "turn the signal down by 6dB", and then they are asking you to reduce the amplitude of that signal by one-half.
Decibels are useful because humans perceive audio levels logarithmically. The logarithmic scale is not linear. If you lot turn upwardly the amplitude of a signal by 6dB, it will exist twice the original aamplitude. If you plough it up another 6dB, it volition be at 4 times the original amplitude. Another 6dB would put it at 8 times the original amplitude. The numbers abound very quickly: if you turn upwards a bespeak past 60dB, its aamplitude will be yard times the original amplitude!
dBu and dBVare decibel units specifically for measuring voltage. Unlike the dB, they are actually units considering they tin can be converted to an bodily voltage value. dBu is dB relative to 0.775 volts; such that 0dBu = 0.775 volts. dBV is dB relative to 1.0 volt; such that 0dBV = 1.0 volt. To chop-chop convert between dBu and dBV notation that dBu is always equal to dBV plus 2.21. The V in dBV is capitalized to provide clarity between Five and u when writing it down.
dB-SPL is a measure of sound force per unit area level in the temper, and is used to measure the amplitude of sounds (audio pressure waves) traveling through the air. 0dB-SPL corresponds to a sound pressure level that is barely aural to the average human. dB-SPL is also a unit of measurement, considering information technology tin can be converted to other units of pressure, like pascals.
dBFS, or decibels relative to Full Scale, is used to measure digital audio signal levels. dBFS is another dimensionless quantity, because it is just a number and cannot be converted to another unit of measurement. In a digital audio system, 0dBFS refers to the maximum point level possible, also known every bit the clipping point. Therefore, dBFS values are always less than or equal to nix. -10dBFS corresponds to a indicate that is 10dB lower than the clipping point of the system.
Full Scale
0dBFS (Full Scale) is the clipping signal for a signal in a digital audio production. Rather than measuring from the racket floor upwards, digital signals are measured (or referenced) from the clipping betoken, or full scale, down. A 0dBFS (Total Calibration) point contains the maximum corporeality of digital information that can be used to correspond the signal beingness defined.
In whatever digital processor, an output driven with a 0dBFS signal should supply the full output potential of the device, annihilation across that level would be clipping the output. Biamp's digital clipping point at +28dBu (top). Thus +28dBu = 0dBFS on a Biamp meter. This may non hold true on other manufacturers' devices, if they accept designed their products effectually a different clipping point.
Headroom is an important concept in audio systems - to maintain proper headroom you need to have enough bachelor signal range remaining in a higher place the RMS bespeak to accommodate peaks without clipping. Clipping is a deformation of the audio waveform as a result of saturating or overdriving the system.
An analog organization will clip when there is no remaining voltage available to describe the louder indicate - it has reached the maximum voltage level the system can reproduce, if it attempts to go louder the loudest parts are "clipped" off. In a digital arrangement clipping occurs when there are no farther data bits available to encode the betoken - information technology results in digital noise or hash.
With Biamp floating-bespeak DSP devices, a indicate greater than +28dBu peak will clip if it exits the DSP via the analog or digital outputs. Signals that are greater than 0dBFS will clip if they are transmitted beyond CobraNet, Dante, AVB, or USB digital sound paths.
For live music performances with large dynamic range, sufficient headroom is usually considered to be 18-20dB. The +4dBu "pro audio" average RMS level plus 20dB of usable headroom for peaks necessitates +24dBu before clipping for musical performance, thus the industry has largely adapted to cover +24dBu as the standard on pro audio devices, at least in Northward America.
To do the math for dBFS, this would hateful your RMS average level should be most -20dBFS, which equals +4dBu (24dBu - 20dB = 4dBu; 0dBFS - 20dB = -20dBFS). This 0dBFS = +24dBu is not a hard and fast dominion beyond all manufacturers, be sure to bank check your equipment to see what the 0dBFS level is referenced to.
Just what about noise floor? A 24-scrap digital audio arrangement (such equally the Biamp DSP) has 144dB of range, so the operating floor of the sampling depth is still 120dB below a -24dBFS betoken. A xvi-bit sample has a range of 96dB, leaving 72dB of downward range. In either case, the dissonance floors presented by the microphones and the environment itself will be your business organization, not the range of usable chip depth.
Analog output settings
(Notation - to see the controls mentioned here in Audia or Nexia software, exist sure to enable Output Attenuation when creating the Output block.)
At Biamp, we reference our meters then 0dB = 0dBu = 0.775 volts when operating at the +24dBu (default) output setting. If a lower Full Scale (dBu) output setting is selected the output voltage is scaled accordingly.
The Biamp analog output phase has selectable fixed settings of -31dBu, 0dBu, 6dBu, 12dBu, 18dBu, or 24dBu. This is a maximum voltage value produced when the analog output is driven to the onset of clipping.
Recall that Biamp shows its clipping point as +24dBu on its meters. A +24dBu (0dBFS) signal will drive the analog output to its maximum voltage. The full calibration digital bespeak is converted to an analog signal at the output block, the dBu setting allows yous to specify the maximum analog voltage delivered by the output.
Changing the Full Scale Out setting will vary the voltage being supplied at the analog output connection. It is important to await at the spec for the next device in the betoken chain to ensure that the voltage being supplied does not exceed its input sensitivity rating.
Within the output block, Level (dB) Out allows you to fine melody the output level before the conversion to an analog bespeak. It modifies the level while information technology is still in the digital domain. Its functionally the aforementioned as a Level control placed in line before the output block.
The -31dBu setting provides a mic level signal from the output.
| Analog output cake settings | Analog output maximum voltage (Vrms) |
| Full Scale (dBu) Out = 24 dBu | 12.282 Vrms |
| Full Scale (dBu) Out = xviii | half-dozen.156 Vrms |
| Full Scale (dBu) Out = 12 | 3.085 Vrms |
| Full Scale (dBu) Out = 6 | 1.546 Vrms |
| Total Scale (dBu) Out = 0 | 0.775 Vrms |
| Full Scale (dBu) Out = -31 | 0.0218 Vrms (21.8 mVrms) |
You have probably heard the terms "pro" level and "consumer" level. Pro level is +4dBu = 1.228V RMS and is typically seen in devices with counterbalanced connections. Consumer level is -10dBV = 0.316V RMS and is typically seen in devices with unbalanced connections. The "level" is an average RMS level for plan material at unity gain point inside the device. Superlative levels can be 20dB or more than above the average RMS level.
"Consumer" level of -10dBV equals -7.7825dBu, and then it is eleven.7825dBu (about 12dBu) less than "pro" level. Annotation information technology is not a "14dB" divergence, since two unlike scales are being referenced (dBV and dBu) you need to catechumen 1 of the values to the same scale as the other and and then await at the difference in level between the two.
VU meters are the ballistic arrow type meter seen on most older analog gear. On professional (studio grade) equipment 0VU = +4dBu. This is why we refer to +4dB every bit "pro level", it is a legacy term from the old days of doing sound and referencing 0 on the VU meters.
At Biamp, we reference our meters so 0dB = 0dBu when operating at the +24dBu (default) output setting.
Analog input sensitivity
The analog input block's Gain In setting allows you lot to set a value from 0dB to +66dB in 6dB increments. This setting is used to lucifer the input sensitivity of the device to the connected source. As y'all enhance the Gain In value, you are amplifying the incoming voltage supplied by an external device. A microphone has a very, very low output voltage relative to a CD player's line out or a mixing console'southward line out then y'all would use a college Gain In value for a mic (amplifying information technology, or "gaining it upward", more), and lower for the line level devices (which need less proceeds increase).
The goal is to bring the voltage up to an average of 0dBu, the nominal operating voltage of the Biamp hardware. This will optimize the incoming voltage level for the D-A conversion hardware - assuring the best signal-to-dissonance and headroom are maintained.
Note that when you set input gain y'all are matching voltage levels between devices, not matching impedance. Impedance matching is not necessary or desirable - the manufacturer has already designed the components to play nicely with other components.
Phan Pwr or Phantom Power is a 48 volt DC current applied to the input circuit to provide ability to a condenser / electret microphone or an agile Direct Box. It should never be used for devices which do not demand phantom power.
When a source device is sending a tone measuring at 0dB on its meters, the input level meters on the receiving device should also read 0dB.
- For a line level device providing +24 dBu (or 12.23 Vrms) maximum output voltage to a Biamp device the correct input gain setting is 0dB. At 0dB an input signal is passed into the Biamp device at unity gain - no proceeds has been added to or subtracted from the indicate.
- For a line level device providing +12 dBu (or 3.065 Vrms) maximum output voltage to a Biamp device the correct input proceeds setting is 12 dB. Since the supplied voltage is decreased y'all demand to increase the input sensitivity.
- For a mic level device providing -31 dBu (or 0.021Vrms) maximum output voltage to a Biamp device the correct input gain setting is +54 dB with a "fine tuning" of +1 dB to match the level of the input. Once more, since the supplied voltage has been decreased you need to increment the input sensitivity to get back to 0dB.
See the chart below; and note that 0dB Proceeds In is non the same thing every bit 0dBu of voltage.
The Biamp DSP can handle a maximum input voltage of +24dBu. A Gain In setting of 0dB means that for a signal that is coming in from a device which also produces a +24dBu maximum level no correction offset is being applied to lucifer the gain structures. For whatsoever device providing an input voltage whose (potential) maximum level is lower than +24dBu we demand to provide an offsetting brand-up gain to bring the clipping points of the two devices into alignment. This applies to any input device, whether it is a microphone, a PC, a codec, a music server, a mixing panel, or some other DSP unit. Similarly, if the device has a maximum output level greater than +24dBu and then that device needs to be attenuated to limit its maximum level to +24dBu.
The Gain In setting is used to match voltages betwixt devices by boosting a lower voltage analog input signal upwards to an average of 0dBu RMS every bit it enters the DSP unit of measurement, just earlier the A-D (analog to digital) conversion.
| "Gain In" Setting (aka - sensitivity) | Input source blazon | dBu (maximum level from the source) | Vrms (maximum level from the source) |
| 0dB | line level | 24 dBu | 12.28 Vrms |
| 6dB | line level | 18 dBu | 6.16 Vrms |
| 12dB | line level | 12 dBu | three.09 Vrms |
| 18dB | line level | half-dozen dBu | 1.55 Vrms |
| 24dB | line level | 0 dBu | 0.775 Vrms |
| 30dB | line level | -6 dBu | 0.388 Vrms |
| 36dB | mic level | -12 dBu | 0.195 Vrms |
| 42dB | mic level | -18 dBu | 0.0975 Vrms (97.5 mVrms) |
| 48dB | mic level | -24 dBu | 0.0489 Vrms (48.9 mVrms) |
| 54dB | mic level | -30 dBu | 0.0245 Vrms (24.5 mVrms) |
| 60dB | mic level | -36 dBu | 0.01228 Vrms (12.28 mVrms) |
| 66dB | mic level | -42 dBu | 0.006156 Vrms (6.156 mVrms) |
Test it
You lot tin can mensurate the peak Vrms output value of the device by connecting a multimeter beyond pins 2 and 3 (+/-) of a line output.
Testing the maximum output voltage
Use a tone generator ready to a 1kHz tone at +24dBu, this can exist wired directly to the output in your layout.
Sine waves have a crest factor of +3dB. If you adhere both a peak meter and an RMS meter to the signal path you will encounter that the RMS meter reports +24dB and the peak meter reports +27dB
Recall with dB that a drop of 6db (-6dB) equals ane/ii the voltage. Adding 6dB equals a doubling of the voltage.
| Source = 1kHz @ +24dBu | Total Scale (dBu) Out = 24 | 12.28Vrms |
| Source = 1kHz @ +24dBu | Total Calibration (dBu) Out = eighteen | six.16Vrms |
| Source = 1kHz @ +24dBu | Full Calibration (dBu) Out = 12 | three.09Vrms |
| Source = 1kHz @ +24dBu | Full Scale (dBu) Out = six | 1.55Vrms |
| Source = 1kHz @ +24dBu | Full Scale (dBu) Out = 0 | 0.775Vrms |
| Source = 1kHz @ +24dBu | Total Calibration (dBu) Out = -31 | 21.8mVrms |
Note: All measurements are made with internal RMS meters reading +24, fed with a 1KHz sine tone. Expect a pocket-size margin of error on your voltage readings since there are tolerance variations in all of the components involved. Differences greater than a few percentage should be cause for farther investigation.
Testing with a +4dBu tone.
A 1kHz tone at 4dB RMS in the Tesira system volition measure roughly 1.23V RMS at the 24dBu output setting, 0.615V RMS at the 18dBu output setting, 0.310V RMS at the 12dBu output setting, 0.155V RMS at the 6dBu output setting, 0.078V RMS at the 0dBu output setting, and 0.002V RMS at the -31dBu (mic level) output setting.
A 1kHz tone at 0dB RMS in the Tesira arrangement volition measure out roughly 0.775V RMS at the 24dBu setting, 0.388V RMS at the 18dBu setting, 0.195V RMS at the 12dBu setting, 0.097V RMS at the 6dBu setting, 0.048V RMS at the 0dBu setting, and 0.001V RMS at the -31dBu setting.
Practical instance - output
We know that the Biamp DSP has a maximum output voltage of +24dBu. Due to differences between products it is possible that this level volition exist likewise high for the input of another device, causing distortion as the input is overloaded. Here are some examples of mismatches.
Case 1:
When we connect information technology to an amplifier nosotros demand to know the specifications for that amp. Here is a sample from a professional person quality amplifier'south data sheet:
Notice the input clipping occurs at +18dBu. If we utilize the total +24dBu potential output of the Biamp nosotros will exist clipping the amplifier on a regular basis, causing the system to sound bad and probably damaging or destroying speakers.
It is necessary to friction match the output voltage of the Biamp DSP to the input voltage of the amplifier. Changing the Biamp DSP'south output setting to +18dBu limits the maximum voltage it volition supply when operating at full volume to a level appropriate to the amplifier's input circuit.
The importance of this calibration becomes clear when we consider setting limiters for an amplifier to protect our speakers. If the amplifier is rated for a +18dBu maximum input signal and the DSP sends a +24dBu point to it the amplifier volition encounter twice the allowable input voltage and volition exist clipping. If you take set up your system limiting in the DSP information technology is possible to be below the limiting threshold level and however be clipping the amplifier inputs and dissentious the attached speakers. It is vitally important to understand the human relationship between the components and recognize that there is not a "standard" for all manufacturers.
Example 2:
Hither is another case where the maximum input voltage immune by an amplifier is well beneath the maximum that the Biamp DSP can provide. In this case a Full Scale (dBu) Out setting of 0dBu (zero dBu) would be the correct 1 to specify. Information technology will allow a maximum of 775mV to be produced by the DSP at maximum level. Now the amplifier'due south attenuation pots (book knobs) can be adjusted for the room without fear of the input bespeak clipping.
Digital input settings - amplifiers
When an amplifier receives its input signal via AVB, CobraNet, or Dante the betoken will come in referenced to 0dB Full Scale (0dBFS).
Equally with analog amplifiers, virtually digital amplifiers volition provide an attenuation command, allowing you lot to reduce the signal level being fed into the amplifier - either via a front panel interface or software interface. This is a line level control, located post-input, before the amplifier stage. The attenuation controls volition take a range of minus infinity to 0dB.
The amplifier may besides accept an amplifier gain setting. Irresolute amp proceeds can be seen as irresolute the amplifier'southward sensitivity, you lot are adjusting the input level that is required to provide maximum rated output power to the connected load. College amplifier gain equals college input sensitivity, meaning a lower input level is required to reach maximum output power. Amp gain primarily affects the corporeality of headroom for the arrangement.
Adjusting proceeds (sensitivity) should be utilized to optimize the ratio of amplifier headroom to racket flooring. At college gain settings (higher sensitivity), more of the noise floor will be amplified and the bachelor headroom before clipping will be lower.
In configuring an amp for the digital input, refer to its transmission to find the optimal setting for your amplifier. In the example shown above, further reading of the transmission reveals that for a Dante digital input the amplifier's attenuation level should be 0dB and the amp gain setting should be 35dB.
Digital output settings - Audia EXPO
The Biamp EXPO, EXPO-4, and EXPI/O-ii are standalone CobraNet devices that can receive digital audio from a transmitting CobraNet device.
EXPO
Output level adjustments on the EXPO (viii-aqueduct, single full rack infinite) are made via analog attenuation pots on the front panel of the device. A pocket-sized flathead screwdriver is the tool required. Fully clockwise will requite +24dBu output, rotating the screw fully counterclockwise will reduce the output voltage to -31dBu (mic level). It is a variable output, there are no detente positions between the 2 limits. To calibrate the analog output of the EXPO to the input of the next device send a 1kHz sine tone at 0dB RMS over CobraNet to the EXPO. Set the next device to its lowest input sensitivity, normally 0dB or line level on the input (and ensure phantom ability is disabled), and so connect the EXPO output to the input of the next device. Observe the input meter of the device: if the meter is above 0dB use the attenuation pot on the EXPO to reduce the betoken to 0dB on the input meter of the new device; if the meter is below 0dB increment the input sensitivity of the new device to enhance the input signal to 0dB.
EXPO-iv and EXPI/O-2
Analog output level adjustments on the 1/2 rack infinite EXPO-4 or EXPI/O-2 are made via the front panel menu under OUTPUT Gain.
Since it is a digital device (CobraNet) the output is referenced from Full Calibration Digital (FSD) or dB Total Scale (dBFS). Recall that 0dBFS is the maximum possible setting, annihilation college would be into digital clipping.
The available settings are 0dB, -6dB, -12dB, -18dB, -24dB and -55dB. These are all dBFS values.
These equate to +24dBu, +18dBu, +12dBu, +6dBu, 0dBu, and -31dBu in the Audia output cake. These are all dBu values.
There is a 24dB outset due to the different scales being used. The analog output voltages of the EXPO remain consistent with what the Audia output cake provides.
Calibrating meter levels to a Yamaha LS9 console
Yamaha digital consoles reference their Total Scale meters to 0dBFS = +24dBu. The correct average level to maintain rubber operating headroom should exist at well-nigh -20dBFS to -24dBFS. The LED colors alter from light-green to orange at -20dBFS (+4dBu) to provide a visual indication of your level.
The Yamaha LS9 tin connect to Tesira via analog connections or digital audio networks (AVB, CobraNet, or Dante)
When continued to the Biamp Tesira a signal registering -24dB on the Yamaha'southward output meters will register as 0dB on the Biamp's input meters.
The meter's reference indicate is unlike in each production. The actual level with respect to the digital clipping point of both products is the aforementioned.
A 0dB output from the Biamp Tesira to a Yamaha panel volition be seen as -24dBFS at the input. This is the correct level. It shows that there is 24dB of headroom remaining before the digital signal clips.
Source: https://support.biamp.com/General/Audio/Gain_structure:_input_and_output_levels
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