Decibel and Meters – V

Where do we find the meter in the most commonly used audio equipment?

Following the path that generally goes through the audio signal we see what common equipment (modern) use the scales in decibels and how.

Premise

There is no defined meter number, the number of meters depends on how many channels / signals we want to control, for example a mono signal will be 1 meter for a stereo signal 2 meter, for a surround or multichannel signal the corresponding meters (6 – 7 – 8 etc.).

Microphones

Generally there are no meter in the microphones, they exist only in some of the radio receivers for wireless microphones (professional one) (fig. 1), jack radio, signal receivers.

Fig. 1 2016-01-08_14-34-50

As can be seen from Figure 1 it is necessary to have a meter that identifies the level of audio signal output from the receiver so that can be attenuated if it is distorted or amplified if it is too low.

The meter of modern wireless microphones are mostly digital meter in which the red LED is the highest one and represents the 0 dBFS, 12,28 V (+ 24 dBu) for the SMPTE standard o 6,16 V (+ 18 dBu ) for the EBU standard.

The output of the analog level signal is generally converted both for a line level output (+ 4 dBu ) that for a microphone level (- 50 dBV ).

 

Stage Box – Splitter

Stage Box – Passive Splitters do not have meters, while Stage Box – Active Splitter (Figures 2 and 3) generally have two LEDs, one green (signal) that lights up when passing the signal and a red (clip) that turn on when the signal is too high and send distortion the active circuit, they are generally True Peak Meters.

Fig. 2 2016-01-08_14-51-15.png Fig. 3 2016-02-12_17-31-30.jpg

The signal level shown by the leds in Stage Box – Active Splitter is a microphone signal which generally ranges from – 65 dBV, – 50 dBV in some cases a few dB most and a few dB less dependent on the type of microphone the choice of construction, up to 0 dB, which represents a line-level values (or, 775 V or 1.224 V).

In Stage Box – Digital Splitter (fig. 4) there is almost always a single meter to which it may be associated with the display of signal for the selected channel, it is a Digital Meter with generally average amplitude scale.

Fig. 4 2016-01-08_15-00-44.png

The signal level represented by the digital meter in the case of analog connections is always after the A / D converter (for the inputs) and before the D / A converter (for outputs) for which in the digital domain, the clips to 0 dB is 12.28 V (+ 24 dBu) for the SMPTE standard or 6,16 V (+ 18 dBu) for the EBU standard (it is therefore of fundamental importance to know the standard used to interface various digital equipment properly).

The inputs of these devices always accept signals with voltage levels of the microphone, and the more the quality will be (we speak of inputs in Stage Box – Active Splitter and Digital) and a lot more tension will be able to withdraw without creating distortions.

The outputs always have a line voltage level with reference at 0 dBu or +4 dBu.

Outboard Processors

Outboards such as Microphone Pre-Amplifiers, Compressors, Gate and Equalizers generally have a signal meter (True Peak meter if analog, Digital Meter if digital) (Figure 5) which identifies the user-selectable input and output signal level Between in and out to decide which display to have, or with two separate meters one for input and one for output. And in the case of Compressors, Gate and other dynamics processors also a meter that displays the GR (Gain Reduction) level, we will see the GR explanation when we talk about dynamic processors.

Fig. 5 2016-01-08_15-10-38.png

The input and output meter of outboard processor always represents the line level signal, so 0 dB is generally at 0.775 V (0 dBu) or 1.224 V (+ 4 dBu).

Some outboard manufacturers that still use valve circuits propose meters as VU Meters (Fig. 6) for both signal and eventual GR. This is because the VU Meter is considered more suitable and more reflects the direction of signal input and output from the valves.

fig. 6 2016-01-08_17-06-27.png

The input of these outboard is microphone level for preamps (in some cases even line) and at line level (in some cases even microphone) for outboard and frequency processors. The outputs are always at the line level.

Audio Mixer

In analog audio mixers, the meter showing the signal level of the inputs (microphone and line preamps) or outputs (line outputs) is a True Peak Meter, in a small mixer it can only be composed of a Green LED for signal and red for signaling distortion level (Figure 7). In professional ones, instead, larger scale is used (Figure 8).

Fig. 7 ZED436_front_on_WhiteBG.jpg Fig. 8 325_6

The level marked by the input and output meter is always with 0 dB indicating 0 dBv or +4 dBu voltage according to the used standard.

n.b. Considering that audio mixers generally have a minimum of 2 channels up to a theoretical maximum of infinity it is easy to think that if I place the signal of each single level of each single channel at 0 dB the sum of all these voltages brings a signal value all ‘Output equal to + infinity (6 dB every doubling of voltage), impossible to evaluate and to put into practice for the interfacing of output signals with input devices. In fact, the matrix circuits that make up the internal mixer structure are built to compensate for these factors and have a signal level at output at 0 dB of 0.775 V or +4 dBu of 1.224 V depending on the standard, independent of the number of channels That goes together. The more the quality will be the compensating circuit, and the more this rule will be respected, on the contrary we will have a mixer that tends to unbalance and create oscillations on the output signals depending on the number of input signals sent.

Generally the meter which indicate the output values have scales greater than those of the inputs unless you have Bar Meter (fig. 9) external who have the task of in detail show the input signal level and output for both analog and digital mixers.

Fig. 9 yamahameterbridge.l.jpg

Generally digital bar meter allow you to act with different display settings like seeing the signal level pre or post EQ, pre or post fader, peak hold and more.

In digital audio mixer the meter are digital as to analyze the digital level signal to both inputs after the A / D converter to which the outputs of the first D / A converter or the digital domain inputs and outputs.

Some manufacturers (especially at the level study and for high-level mixer) propose meter with liquid crystal display and without color gradations holding them higher performance in representing the peak signal values (Fig. 10).

Fig. 10 2016-01-09_14-46-31.png

The first digital mixers had the input and the analog meter then with the presence of a pre-amplifier at the input, which signal was controlled and operated by an analog True Peak Meter and then converted and controlled in digital domain.

The most modern digital mixers have a pre-amplifier at the input whose gain and meter are controlled logically (digital) (Figure 11) (Figure 12), in practice the amplification is done via a logic rotary button As shown in Figure 11) that sends pulses to the amplifier corresponding to the level of rotation imposed and the amplifier responds by amplifying the signal according to the received pulse level. Always this logic controller is also used to manage remote amplifiers, so not just those in the audio mixer but also the Digital Box Stage Amplifiers.

Fig. 11 2016-01-09_13-56-58.png Fig. 12 2016-01-09_14-09-40

Even the digital mixer especially in low- and middle level have the output meter (fig. 13) with a larger scale than that of the input meter.

Fig. 13 2016-01-09_14-14-01.png

Always digital mixers have very often display no-touch or touch screen (fig. 13) with which the user can see and interact with the various audio mixer control parameters (input, output, routing, plugin and other), in which it is also present meter for visualization and management of the input and output levels (fig. 14).

Fig. 14 DSC_0412

The meters contained in the displays of digital audio mixer are Digital Meter Software.

Some mixers have a mix of all these meters (especially those professional digital) and other vintage-style show for each input channel or generally only for VU Meter outputs.

n.b. It is very important that the line output level from the audio mixer as main or aux out audio has an average level (always illuminated LEDs) that arrive at a maximum of 0 dB this to not overload the output circuit itself especially if it is active. Levels above 0 dB are mostly accepted as signal peaks (LEDs that only light up in the presence of such peaks) (if this does not distort the input to which this signal is sent), but if possible avoid (Because of the drop in quality and risk of faster wear of the components themselves). Even more, avoid sending a signal level that brings “red” overload values, since in addition to generating a distorted signal there is the easy risk of breaking the output circuit itself.

If you need more “volume” it is highly recommended to increase the overall power of the audio system.

 

Power Amplifiers

In a PRO level the power amplifier is the audio amplifier which has the task of raising the signal line to that power from transmits to the speaker for the diffusion.

Work always in the analog domain apart some with eventual signal processing and amplification on the digital level especially in the most modern amplifiers, and the meter generally in small scale are True Peak Meter for analog systems, digital meter for digital ones or a mix of both (fig. 15).

Fig. 15 2016-01-08_17-19-53.png

They have a green light for the signal and another green light to display the ignition, one red for the clip and then when the end goes into distortion and a red or orange when out protection to prevent breakage.

They have a green light for the green signal and another to display the ignition, a red one for the clip, so when the amplifier goes into distortion and a red or orange when out protection to prevent breakage.

The input signal is at 0 dBu or +4 dBu.

In more modern ones (fig. 16) there are graphical displays where you can choose various setup parameters for viewing, usually on Meter Software (as we shall see later in this article) and have almost always True Peak Meter to wider scale.

n.b. The level to be sent to the power end inputs (which is generally the output signal at the line level of audio mixers) is that of the required operating standard, generally 0 dBu (0.775 V) or +4 dBu (1.223 V) and This as we said before is important that the signal level output from the mixer has at least a maximum rms value at 0 dB, this so as not to create any distortion values for either too much signal sent or for generating different impedance values between Final input circuit and mixer output circuit which lead to instability and frequency response alterations with high quality leaks (especially if the circuit is serviced or active). It is possible to send signal peaks beyond 0 dB, but be careful that the final meter does not reach distortion values (red led), since in case of overheating the components that make it can easily go to protection (switch off for precaution in order to allow it to cool down to avoid damaging the amplifier components), or in the long run, the components may break, as well as requiring power output to output a very high voltage value that could Also bring the audio speaker to the break.

Fig. 16 2016-01-08_17-50-12.png

 

Audio Speakers

The passive audio speakers do not present meter, while those active (fig. 17) have meter or LEDs that show the input signal in the power amplifier as seen before.

Fig. 17 2016-01-08_17-54-49.png

 

Other

Also multitrack recorders (Figure 18), A / D – D / A converters, World Clock generators (Figure 20), Digital Patchbay (Fig. 21) have mostly Digital Meters or LED bars that identify the Presence and circulation of the signal, any current sampling information, and any signal routing information.

Fig. 18 avid_hd_io_front_1.jpg

Fig. 19 61517.jpg

Fig. 20 Brainstorm-DCD-8-front

Fig. 21 products_madi_router_3b

In the case of use of plugins (fig. 22) DAW (fig. 23) or Applications for remote control example of digital audio mixers (fig. 24), then we talk about software, these always have digital meter on software.

Fig. 22 2016-01-08_17-57-13.png

Fig. 23 2016-01-08_18-01-01.png

Fig. 24 screen480x480

n.b. Some meters in digital software have the 0 dBFS value, but they also have positive values (fig. 25), sometimes even up to + 6 dBFS. The maximum value of the digital signal remains, however, 0 dBFS beyond which it begins to distort, only at the software level it is possible to control these distortion levels, so if the distortion that is generated is not annoying or remains with a background noise very low, if necessary, digitally amplify the signal value by further raising the control fader (this even more if signal processing is floating point as we will see when we talk about digital audio). While other software if they were built to be interfaced with analog devices (example daw for recording) they place an analog meter number scale (figure 23) but with scale and response from Digital Meter.

Fig. 25 2016-01-08_18-09-59

 

Conclusions

In addition to the meter as we’ll see in future arguments, there are other systems mostly software that allow to analyze the decibels and the sound spectrum, such as Sound Level Meters, Charts FFT and RTA, Impulse Response, Spectrogram, Transfer Function, and more.

Other details can be found in these two articles on the web:

Loudness Metering and – I

Loudness Metering and – II

Some standards for measuring digital audio equipment are defined by the standard AES17.

 

More on Decibel and Meter:

Decibel and Meter – I ( Decibel and Standard Types )

Decibel and Meter – II ( Analog Meters )

Decibel and Meter – III ( Digital Meters and Software )

Decibel and Meter – IV ( Normalization and LUFS Meter )

Decibel and Meter – VI ( Loudness Manager, Loudness Engineer )

 

Some manufacturers of audio hardware, software and plugin meters:

  • Ashdown Engineering
  • Avid
  • Blue Cat Audio
  • Brainworx
  • Coleman Audio
  • Crookwood
  • Cymatic Audio
  • DK Technologies
  • Dorrough
  • Flux
  • Grimm Audio
  • Iz Corp
  • Izotope
  • JLM Audio
  • Logitek
  • Meter Plugs
  • Metric Halo
  • Nugen Audio
  • Orban
  • PSP
  • TC Electronic
  • Teac
  • Slate Digital
  • Sonnox
  • SSL
  • The t.rack
  • Universal Audio
  • Voxengo
  • Waves
  • Wohler
Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s