# Tag Info

## Hot answers tagged amplitude

### When concatenating sine waves, how do I phase shift in order to prevent "pops" caused by sudden jumps in amplitude?

Phase continuous transitions can be accomplished by implementing the waveform in phase versus time instead of frequency versus time. Frequency is the time derivative of phase, so instead of stepping ...
• 52.8k
Accepted

### What is the audible level for digital audio dB units?

The confusion arises from the fact that the decibel (dB) is a relative unit of measurement, not an absolute one. The dB scale in audio can reference different things depending on the context, which ...
• 1,573
Accepted

### Amplitude modulation vs sampling rate?

The OP's opening statement is incorrect: $f_s > f_{max}/2$ prevents frequency aliasing for a bandlimited signal, but not amplitude aliasing $f_s > 2 f_{max}$ prevents aliasing. It's as simple ...
• 52.8k
Accepted

### Understanding FFTs for simple Circular Function (sin/cos)

Creating the Frequency Vector The arrangement of the output of fft() depends on whether you use an odd or even number of points for your fft. I think this post nicely summarises how the frequencies ...
• 681

### What is the audible level for digital audio dB units?

dB is a logarithmic metric against a well defined reference. There are many different types of "dB" depending on the nature of the signal. For example voltage measurements can be in dBv, dBu,...
• 46.2k
Accepted

### What is the (approximate) function for amplitude of a plucked string over time? Does it differ between string types?

An exponentially decaying envelope $a\exp(-b x)$ is a good choice, and is used for example in vintage Yamaha FM synthesizers. It has the favorable property that over any constant length time interval, ...
• 13.6k

### What is the audible level for digital audio dB units?

There's one broad standard that is only strictly followed in certain conditions. The cinema standard is a 500-2000 Hz band-limited pink noise signal with digital RMS amplitude of -20 dB full scale ...
• 171

### Difference between single sided and double sided amplitude spectrum

For real-valued signals, the frequency spectrum is conjugate symmetric; i.e., $$X(f) = X(-f)^*$$ This translates into an even magnitude spectrum $$|X(f)| = |X(-f)|$$ and an odd phase spectrum. Because ...
• 28.3k
Accepted

### Can FFT tells us existance of same frequencies with different phases?

I am thinking of two numbers. They add to the number 15. Tell me what the two numbers are.

### What causes the mismatch between a calculated sine wave and a measured sine wave?

Sorry, can't reproduce. I did the same thing with the dither turned off and found a perfect match between the generated sine wave and the calculated values. Even with a dither turned on things were ...
• 46.2k

### Equal power crossfade

This is a continuation of the (music-dsp) thread started by Element Green titled: "Algorithms for finding seamless loops in audio" As far as I know, it is not published anywhere, although I ...
Accepted

### Quadrature modulation for FM and AM

Both amplitude and frequency modulated radio signals nowadays use quadrature modulation and demodulation as a mean to transfer and receive radio signals. This question is ill-defined â€“ a signal ...
• 31.6k

### Do DCT results contain phase spectrum?

A DCT is equivalent to a DFT of real data that is doubled and mirrored, thus rendering it symmetric. The DFT of any symmetric real signal has a phase of zero (its all cosines, no antisymmetric sine ...
• 35.5k

• 52.8k

### Amplitude modulation vs sampling rate?

The claim is wrong. Sampling of a pure sinusodial whose frequency is below but arbitrarily close to the Nyquist frequency (half the sampling frequency) is a perfectly valid operation, as long as you ...
• 28.3k

### Relationship between amplitude and sampling rate

In order to resample without aliasing, the resampling process needs to apply an anti aliasing filter at the new Nyquist Frequency (or thereabouts). So chances are, your resampling process applied a ...
• 46.2k

### Is digital necessarily discrete in both amplitude and time?

It's a matter of definition. Usually one defines digital to be discrete in both, discrete time to be (possibly) amplitude continuous and quantized to be (possibly) time continuous.
• 231

### When concatenating sine waves, how do I phase shift in order to prevent "pops" caused by sudden jumps in amplitude?

IMO the best way to implement this is a rotating phasor. Recall that $$e^{jx} = \cos(x) + j \cdot \sin(x)$$ and $$e^{j\omega(n+1) } = e^{j\omega n } e^{j\omega}$$ That means we can calculate the a ...
• 46.2k

### Why MATLAB's abs(fft(X)) returns maximum amplitude first harmonic's while in signal maximum is second's?

Spectral leakage. In order for FFT of a sine wave to be a single line, the sine wave must have an integer multiple of periods in the FFT window. Try the following ...
• 46.2k

### Closest two frequencies that can be resolved

There is no issue of frequency resolution in a typical modulation and demodulation scheme. (unless you want to implement some frequency/signal detectors) Putting two message signals in adjacent ...
• 28.3k
Accepted

### First-Order Hold Filter Gain

That's correct, $0.4053$ is the approximate magnitude of the frequency response of linear interpolation at the Nyquist frequency. With the definition: \operatorname{sinc}(x) = \frac{\sin(\pi x)}{\...
• 13.6k
Accepted

### Amplitude loss during resampling with IIR

Try adding a gain of 16 before your low pass filter, or equivalently using a low pass filter with a passband gain of 16 instead of 1.
• 46

### A clarinet has no even harmonics. What would produce no odd harmonics?

The clarinet has no even numbered harmonics up from its lowest pitch because of its shape. It is open at one end (the bell) and effectively closed at the other (the mouthpiece). This causes the ...
Accepted

### Help me understand how Pulse-Amplitude Modulation (PAM) works

If you define pulse amplitude modulation (PAM) as a method where a train of pulses is generated with the information coded by the amplitude of these pulses then both methods comply with that ...
• 90.6k
Accepted

### Lock-in amplifier

The answer to your questions is yes, at least for the ideal situation. My simulation is presented below, with the following assumptions: 1) the small signal is a sinewave at 12.5 Hz, with 10 mV peak ...
• 795