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

learn more… | top users | synonyms

1
vote
1answer
39 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 ...
0
votes
0answers
46 views

What does it mean for a voltage to be attenuated by X dB [duplicate]

Say that a signal is passing through a medium, and in the middle of it, the amplitude of that signal drops by 90%, in this case I would just say that the media attenuates the amplitude by X factor. ...
1
vote
2answers
92 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 ...
0
votes
2answers
145 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?
0
votes
1answer
62 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 ...
0
votes
4answers
89 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 ...
0
votes
0answers
490 views

dB Meter with Arduino and AD8307

I am attempting to construct a decibel meter using an electret mic breakout board (shown below) and an AD8307. If necessary I can use just an electret mic, and not the breakout board. I was ...
4
votes
1answer
297 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 ...
5
votes
3answers
189 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 ...
1
vote
2answers
307 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 ...
2
votes
1answer
201 views

Calculating the voltage generated by an 40KHZ Ultrasonic Tranceiver

In particular, this device: http://www.hexamite.com/hx40str.htm ...
5
votes
4answers
305 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 ...
9
votes
8answers
2k views

Why Decibels are used to measure Signal to Noise Ratio?

We just started a communications course in college and we came across SN ratio. The following is an ambiguity I am facing which my professor is unable to resolve: Signal to Noise Ratio is the ratio ...
0
votes
1answer
279 views

Relationship between FFT in dB and spectrum analyser output in dBm

I am trying to calibrate my RF daughter board in USRP software defined radio. I am trying to measure transmitted power for different frequencies at a certain set gain and transmitter amplitude. When I ...
6
votes
4answers
731 views

Confusion between Voltage gain & Voltage gain in decibels (dB)

The definition of the Voltage Gain is \$ V_{out} \over V_{in} \$. However, I read some articles about the gain in decibels, and I have a confusion now. Here is an article about it: ...
1
vote
4answers
483 views

Headphones impedance and the SPL

The headphones A has an impedance of 32 Ohms. The headphones B has an impedance of 250 Ohms. Both of the headphones are similar by size. Is it right that the headphones B will play quieter by ...
6
votes
5answers
1k views

What does it mean for a signal to have an amplitude below 0 dB?

I am a software developer (using high level languages like .NET,C,C++ etc) trying to understand how computers work at a lower level. I understand that amplitude is always positive because it is ...
1
vote
1answer
86 views

Power and decibels

In one of the examples in a engineering textbook, I noticed that the decibel value for the Power of a transmitter (also known as modulator) was 20DB and this was said to be equivalent to 100W. ...
3
votes
3answers
520 views

What do you call the dynamic range of a variable gain amp?

Dynamic range is the ratio of the largest signal a system can process to the noise floor of that system. If the system has variable gain, though, then you could interpret this two ways: Fixed gain ...
6
votes
4answers
1k views

Why do we use dB to represent the difference between two voltages?

For example, the passband of a LC resonant circuit is the differences of frequency at +3db and -3db. Why do we prefer dB?
8
votes
4answers
9k views

What is the significance of -3dB?

My oscilloscope has 100 MHz -3dB bandwidth. -3dB is 0.707 units (sqrt(2) / 2). What does this mean, why 70.7% attenuation? Is there any particular reason for this attenuation level?
20
votes
5answers
4k views

What does dBm mean?

When working with radios, I've seen the term "dBm". What does this mean? The wikipedia page gives a table showing the equivalent power in Watts. Is the dBm output just the power level of a ...