# Questions tagged [decibel]

Anything related to the decibel (dB) and similar logarithmic units of measurements (dBm, dBW, etc.).

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### How can I get 110 dB from a 10 or 15 mm piezo?

I’m trying to get the loudest sound possible out of a 10 or 15 mm piezo. I got 120 dB from a 20 mm piezo with 12 V but hoping to get the same sound from a smaller size. Any suggestions?
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### Noise decibel meter - how to convert MAX4466 voltage output to unweighted dB(SPL)

Using this microcontroller with that electret microphone amplifier, I want to build an unweighted dB(SPL) meter as good as it can get - then compare it to this ready made breakout board, this NIOSH ...
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### KY038 sound sensor: Voltage to SPL

I'm writing code to measure frequencies with a KY038 microphone sound sensor. It uses an LM393 voltage comparator. How do I convert voltage to sound pressure level (SPL)?
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### Conversion of radio emissions to decibels and role of impedance ratio to power ratio

This question is about a web article about radio noise suppression by Ferrite beads. The above diagram plots of a family of four curves for the ferrite bead. Each curve depicts the relation of ...
2k views

### Is there any way to measure sound intensity in decibels without using a microphone?

I am trying to measure sound intensity in decibels without using microphone in a home automation project. Due to privacy concerns, I don't want to use a microphone in the device. Is there any way I ...
106 views

### How does dB apply for non-linear components?

I understand that decibels are used to express power and we can use 20log(V1/V2) and 10log(P1/P2) to find the voltage and power ratios. But what are we meant to do when it comes to non-linear ...
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### How to convert from datasheet dB value to pressure per volt?

I am trying to measure sound waves using a Raspberry Pi Pico ADC pin but am having trouble converting the sensitivity value on my data sheet into pressure units per volt. I have read a many articles ...
3k views

### Convert dB to ohms

I did some impedance measurements in high frequencies using a VNA. I did not pay attention to the format of the measured values that were in dB so it is now to late for me to reperform measurements. I ...
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### How to interpret this type of dBm?

I have encountered a spec of a laser diode given in dBm/nm instead of dBm: If I want to know the average power between 2065nm and 2075nm, would the integral of that section give the average power in ...
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### Valid or invalid logarithm operation?

Is the following operation valid or invalid? The question is to calculate receiver gain and this is one of the steps I got confused. The receiver sensitivity is given -45dBm and transmitted power is ...
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### What happens when we reach the maximun atenuation in Optical Networks Terminals (Optical fiber )?

Let´s suppose We have the following Optical Network Terminal : According to datasheet, the receiver sensitivity is : -27 dBm Now Let´s suppose We have the following fiber optical network : As we ...
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### Meaning of dB units in periodogram (FFT)

When I calculate spectrum of a voltage signal using FFT and then I calculate periodogram using $$S_k=10\cdot log_{10}(\frac{1}{N}|X_k|^2)$$ where $X_k$ if the result of FFT and $N$ is number of ...
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### Scale dB SPL based on mic sensitivity

I have a measurement performed using GRAS 46AE microphone calibrated at 410mVrms at 114dB (250Hz). I have a .wav file recorded and performed stft and obtained the magnitude. Now I would like to scale ...
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### Sound level meter using a microphone with ADC

I'm working with STM32F4, MAX4466 amplifier and a condenser microphone. In other words, Adafruit 1063. I want to get the sound level in dB unit. I know: Microphone sensitivity: 0.0063096 V/Pa ...
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### Where does this decibel equation come from, why a factor of 20?

For sound levels, it is said that decibels follow this equation: $$dB = 20 \log(\frac{p_s}{p_0})$$ Where $p_s$ is the pressure of the measured sound wave (in Pascals) and $p_0$ is some fixed ...
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### How to solve decibels? [duplicate]

If a microphone has an output voltage of 1.45mV @ 1 Pa and a microphone preamplifier adds 50dB of gain, what would the voltage at the output of the mic pre be, ...
163 views

### If a microphone has an output voltage of 2.5mV @ 1Pa, what would its output voltage be when 98dB SPL is applied to the diaphragm?

Microphone spec sheets specify a microphone’s sensitivity by displaying the voltage at the output of the microphone when 1 Pa is applied to the diaphragm. If a ...
2k views

### What is the meaning of dBi?

When we say, for example, an antenna has spec of 22 dBi; Does it mean that its power is 22 dB stronger for any point at fixed direction than if it were to emit spherically?
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### dB scale in LTspice

I have a question about the dB scale in Ltspice. As far as I know it uses 1 of the unit (so 1V in case of Voltage) as a reference and then plots the dB value, which is defined by 20*log(V/Vref). (So ...
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### How to scale audio signal from PCM data to a dB SPL value?

0 I've got a set with MEMS microphones that measure audio signals at ultrasonic frequencies. The MEMS microphones have a PDM output which is then converted into PCM (this is necessary to allow for a ...
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### How to convert dBm to V/m, A/m², and W/m²

Currently I am using a spectrum analyser (SA) Keysight N9020, with an antenna to get readings off the air. The reading on the SA gives a reading of a unit, dBm. However, I need to convert dBm to V/m, ...
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### What does a Bode plot represent and what is a pole and zero of a Bode plot?

I studied Bode plots and the author of my book is somehow relating zeros of transfer functions to Bode plots. What is the relation between zeros or poles of a Bode plot and transfer function? We ...
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### dBA conversion into dB or dB SPL

I saw many websites that how to convert dBA sound to Db and dB SPL conversion. but I did not find any such relationship to convert dBA into dB or dBSPL. Is there any such formula or relationship that ...
963 views

### 3dB frequency of inverting amplifier

There is already a similar question in this website, but I still can't solve this. I have the following information: An inverting opamp with nominal gain -20V/V, DC gain 10^4 and unit gain 10^6Hz. I ...
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### What does that statement exactly mean? ( about dB )

When you separate the collected signals, each car’s channel must attenuate the other cars’ signals at least by 20 dB. A speaker will be able to generate a sound which contains 3 different frequency ...
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### What's the reference dB level in a spectrum analyser?

I am using a spectrum analyser to measure the 248kHz buck switching frequency and its harmonics in my board. I have set the frequency range from 200kHz and 1MHz and I am using a near field H-probe. ...
2k views

### Why -3 dB in signal to noise ratio (SNR)

I'm reading about a signal to noise ratio (SNR), I'm quite new to this kind of stuff. $$SNR=10\log_{10}\left(\frac{P_{SIGNAL}}{P_{NOISE}}\right)=20\log_{10}\left(\frac{A_{SIGNAL}}{A_{NOISE}}\right)$$ ...
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### Why is the microphone output level not proportional to the sound level?

I set up a system to measure the sound pressure level in a location. This consists of a Knowles SPU0410LR5H-QB microphone connected to the codec SGTL5000, which is connected to the micro-controller ...
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### Understanding function generator output when units are in dBm

I am using a function generator with output in units of dBm. It has an output impedance of 50 ohms. I am measuring this output on an oscilloscope, and am failing to understand the waveform's amplitude....
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### Finding the gain difference for a ultrasonic assembly

I am tuning an ultrasonic assembly for a welding application and tuned the system to operate at 41kHz according to the oscilloscope. The transducer operates at 40kHz, when calculating the gain with ...
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### Convert -dB to equivalent +dB

I asked this question on stackoverflow and stackexchange mathematics, but on both sites my question was closed and suggested to ask here as mentioned in the comments to this question on mathematics. ...
821 views

### The unit that is written between parentheses alongside the dB

What is the meaning of the unit that is written between parentheses alongside the dB unit? For example 2 dB (mW) or 2 dB (uW)? What exactly does this unit refer to? Does it refers to the unit of the ...
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### The importance of Decibels [duplicate]

I have a question , why decibels are useful for electrical engineers ?? I still can't figure out why it is useful to use decibels in expressing power ratios , gain and other things ?
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### What is the proper dB unit to use when expressing the amplitude of a sample in a digital audio recording?

I've seen 20*Log10(amplitude) as the proper way to calculate dB, where 0 < amplitude <= 1. (So, to get amplitude when signed integer data types are used to represent amplitudes, you use value/...
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### Audio Frequency Response Offset in dB

Say I have some audio device with the following absolute frequency response: I want to shift the curve up, so that the 1kHz point is the 0dB point, and everything else is relative to this point. Am I ...
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### Calculate linear phase when given in decibel

The datasheet of the LT6230 shows the op amp's phase lag in decibels (page 14). The datasheet does not give a formula to recalculate the angle in degrees, so can I just assume the following being the ...
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### Receiving power from antenna (Homework)

The question: "At a carrier frequency of 2 GHz, assuming a transmit antenna gain of 3 dBi and a receive antenna gain of 0 dBi, calculate the line-of-sight received power at a distance of 100 m from ...
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### Conversion from dBm to dB$\mu$V?

I am trying to derive the conversion from dBm to dB$\mu$V. So, please correct me If I am wrong. \begin{align} \textrm{dBm} &= 10 \log_{10} \left( \frac{P}{1\textrm{mW}} \right) = 10 \log(P) + ...
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### Is the 3dB turnover and 45° correspondence only valid for low pass filter transfer function?

I have been reading at some systems that at 3dB point the phase shift becomes 45°. But is this fact only valid for low pass filters?
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### Are these equations correct? (transfer function)

I have a given transfer function $|H| = \frac{R_2}{\sqrt{R_1^2+\frac{1}{(\omega c)^2}}}$ where $c = 1\mathrm{\mu F}$ and $R_1,R_2$ are unknown. I know that $|H(j\omega_c)| = 50.1$ ...
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### Convert dB to resistance

I am new to this, but I wanted to ask how it would be possible to convert a dB value into resistance. I've been looking at an isolated analog switch from http://www.ti.com/lit/ds/symlink/ts5a3359.pdf ...
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### Units for fourier transform of measured voltage

I have a measured voltage signal that I want to present in the frequency domain. My current process is to take the FFT of the signal, then use $20 \text{log}_{10}|X|$ where $|X|$ is the magnitude ...
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### Converting arbitrary mic input number to dB SPL

I'm trying to convert an arbitrary input number from a laptop microphone into SPL. The microphone specs are available on https://docs-emea.rs-online.com/webdocs/105f/0900766b8105f0e3.pdf. From what I'...
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### A confusion with power ratio jargon used in antenna directivity (dBi/dBd)

Below is an excerpt from a book: Two common terms you'll hear in specifying the gain of an antenna are dBi and dBd. These terms are defined as dB of gain referenced to an Isotrope (dBi) and dB of ...
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### The Output of High/Low Pass filters and the DB changes that occur

I recently just learned what a dB is (decibel) and am trying to figure out why in high/low pass filters these drops occur. Also how they're affected. Say I have a high pass filter with a cutoff ...
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### How does doubling the voltage amplitude change the decibels?

Suppose I listen to some music on my headphones. Now change the amplitude (in volts, as measured e.g. with an oscilloscope) of the audio signal by a constant factor G. Assuming that the amplifier in ...
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### How to calculate PWM duty cycle to compensate for different piezo sounder response at different frequencies?

How to calculate PWM duty cycle to compensate for different piezo sounder response at different frequencies? I have a piezo sounder, and the datasheet informs me that I will get the following ...
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### Meaning of dB while dealing with amplifier(Op-Amp)

I have found a question in MIT open-course material.The question is to Design an amplifier(Op-Amp) with a gain of 20dB While searching about ...
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### SNR and attenuation question

I have the question above from random material and I tried to solve it. Here, I assume signal power to be S1(dB) and noise power to be N1(dB) at input, and S2(dB) and N2(dB) at output. So below is ...
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