# Questions tagged [decibel]

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

60 questions
0answers
18 views

### 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 ...
3answers
62 views

### 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. ...
1answer
730 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 ...
2answers
62 views

### 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 ?
2answers
80 views

### 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/...
1answer
43 views

### 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 ...
2answers
39 views

### Calculate linear phase when given in decibel

The datasheet of the LT6230 shows the opamps 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 ...
2answers
96 views

### 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 ...
2answers
130 views

### 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) + ...
0answers
31 views

### 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?
1answer
81 views

### 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 $|H(j\omega_c)| = 50.1$ ...
1answer
73 views

### 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 ...
4answers
712 views

### 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 ...
2answers
192 views

### 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'...
1answer
211 views

### 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 ...
0answers
33 views

### 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 ...
2answers
772 views

### 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 ...
1answer
335 views

### 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 ...
3answers
747 views

### 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 ...
1answer
778 views

### SNR and Attenuation Question

Hello, I have a question above from random material and 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 ...
1answer
533 views

### Electret microphone - How to Reduce sensitivity

I am doing a classic LED - sound reactive project. The only thing that is bothering me is that my electret microphone (MAX4466 from adafruit) is clipping, and it is because the maximum gain of this ...
1answer
141 views

### Complex RSSI dBm calculations with shield

I have a little bit of problem understanding complex attenuation calculations when there is a shield involved between the transmitter and the receiver. Let's take a simple example: We have a ...
2answers
3k views

### Calculate necessary attenuation (in dB) to achieve a given output voltage

I need to connect an audio unit with an output of 2V (and an output impedance of 560 ohms) to an amplifier with input sensitivity of 0.985V. Since the 2V output is too high for the amplifier, I need ...
0answers
441 views

### conversion dB into dB SPL

I'm using a sound calibrator (1kHz, 114dB SPL, GRAS Type 42AB). When I got my data from my scope, the signal has 5mV. In spectrum mode, it is -50dB at the peak of 1kHz. I'm using this preamp: GRAS ...
4answers
453 views

### Exact meaning of dB?

I know that when people say that a gain of amplifier is X dB, they mean that 10*log(Pout/Pin). However, How can I interpret it when they say that "noise floor is -120dB"? How can I derive voltage ...
1answer
49 views

### Relation between bels and decibles

Following is a sreenshot from "Fundamentals of electric circuits by Alexander and Sadiku". In 14.4 he defines "bels" and then in 14.5 the "decibels". I don't understand the line just above 14.5 that ...
1answer
662 views

### Understanding microphone sensitivity

My goal is to figure out a relation between output voltage and input SPL: $$dB(SPL) = f(V_{out})$$ First, I get the sensitivity in volts from this formula: Sensitivity_{dB(V)} = 20 * log_{10} (...
1answer
63 views

### How to lower volume on microphone input before outputting through headphones? (Using a DSP) [closed]

As part of a senior engineering course, my partner and I decided on tackling the problem of hearing loss in youth, and went with a more preventative approach, trying to reduce the amount of cases ...
1answer
2k views

### Beacon: dBm power decrease over distance

I have beacons which advertise their configured data periodically through Bluetooth. The vendor specifies 8 different power options 0 to 7: https://support.kontakt.io/hc/en-gb/articles/201621521-...
0answers
57 views

### Unity Op amp Question Gain and Resistances

The Question asks what is the gain in dB and also what are the input and output resistances I know the gain is 1 so dB that would be equal to 0 dB But I am confused on how to find the input and ...
1answer
58 views

### Formula for amplitude of volatge, decibell

There is a formula for power 1 and power 2 to convert to decibell. 10*log(P1/P2), but when I have a amplitude of voltage in DC, formula is 2*10*log(U1max/U2max). Why is there a 2? Thanks.
2answers
906 views

### average of dBs or dB of average?

In several papers, books etc. I have encountered to expression of "average gain of the path is ... dB", now I wonder this is the average of dBs or dB of averages? The sources have not mentioned ...
2answers
4k views

### How to get output voltage of microphone?

I am really confused at this moment. I have the following microphone: http://www.farnell.com/datasheets/1660938.pdf What I want to do is make a actual dB meter with this sensor. So I would net to ...
3answers
1k views

### Types of decibels

Why we use dBA or any other type of decibel unit instead of basic decibels unit (dB)? Why we have so many types of this unit?
4answers
249 views

### Is it voltage or power of the signal amplified when the opamp amplification is given in dB unit?

Today, one of my colleague said that he entered a preliminary examination in a company after his job application. One of the questions is exactly "Design a non-inverting amplifier with 20dB gain.". ...
3answers
330 views

### Are ten 2W speakers as loud as two 10W speakers?

If all things are the same (e.g. total magnet weight, manufacturer, cone material) and I have two 10W speakers as compared to ten 2W speakers would the decibel level be the same?
4answers
1k views

### Frequency to dB

As I understand for a sound wave the intensity is determined by the amplitude, frequency and properties of the space, but for amplifiers I have seen that the gain is expressed in dB and is a function ...
8answers
2k views

### Is the meaning of a Decibel different when applied to Voltage vs Watts?

If I have an amplifier that provides +3dB, or an attenuator that provides -20dB, then how do I know if that applies to Voltage or power? In other words, if I have a 0dBV signal and I run it though a +...
2answers
225 views

### How dBuV value changes with distance?

I've got an emissions source that's designed to generate a peak at a certain frequency that when measured by an antenna 3m away gives a value of X dBuV. If the emissions source if moved closer to ...
2answers
27k views

### Why 10Log(p1/p2) and 20Log(v1/v2)? Why not just 10Log(x1/x2)? [duplicate]

Based on my very basic current understanding of decibels in electronics, it is said that I should use the db = 10Log(p1/p2) formula if I want to calculate the power ...
1answer
2k views

### Choosing sampling rate according to the bandwith reponse in accelerometer datasheet

In an accelerometer's datasheet, the bandwidth response in the x and y axis is 350 Hz. There is another information related to the internal sampling rate (shown below). I don't know how these two ...
2answers
3k views

### What is Sensitivity in an ultrasonic transducer Specification?

So far I understand that Sensitivity of the transducer is defined as the ratio of its electrical output to mechanical input. While going through ultrasonic transducer specs, they have a rated ...
2answers
2k views

### Does the VU meter on audio amplifiers measure the input or output level?

Does the VU meter on commercial audio amplifiers measure the level of the input signal or the level of the amplified signal?
1answer
271 views

### G.711 for dummies

I am in midst of some online telephony course, and there are questions regarding which I have no one to ask but this community. G.711 volume encoding. I have some difficulty to understand how exactly ...
4answers
842 views

### Decibel vs Decibel milliwatts [duplicate]

What are the differences between Decibel (dB) and Decibel milliwatts (dBm)? I'm most interested in dBm with cell phone signal strength. Please give a detailed explanation. I'm not familiar with the ...
1answer
429 views

### -3dB on filters, just approximated?

I have been told that -3dB is when you get half the power or equivalently the original voltage divided by the square root of 2. Nonetheless, doing the calculations I get 3.01029dB. I figure this is ...
3answers
255 views

### mW or W when calculating decibels

In my instrumentation class we have been given the following formula to get the power in decibels: $10Log(Power(mW)/mW)$ I'd like to know if taking the power in miliwatts is something widely done ...
2answers
2k views

### I'm confused by the formulas for power gain decibels and voltage gain decibels [duplicate]

I know that my problem with this is some flaw in my logic, I just need someone to point out to me where that flaw is. According to the Wikipedia article, there are different formulas because power ...
1answer
1k views

### Calculating the voltage generated by an 40KHZ Ultrasonic Tranceiver

In particular, this device: http://www.hexamite.com/hx40str.htm ...
4answers
3k views

### Why do 16 bit systems have a minimum dBFS of -96?

I'm working through the example on this page: http://chimera.labs.oreilly.com/books/1234000001552/ch03.html I totally understand why the maximum level of an audio system would be 0 because the log of ...