# Tag Info

### Is sound the best way to transmit a signal under water?

Yes, it is called acoustic communications. Iterative Carrier Frequency Offset and Channel Estimation for Underwater Acoustic OFDM Systems is an example of a paper that uses orthogonal frequency ...

### Acoustic waves propagation distance relation with carrier frequency?

For a sine wave of amplitude $A$ and frequency $f=1/T$, its energy from $-T/2$ to $T/2$ is $A^2T/2$. Thus the power depends only on amplitude. The energy over one period does depend on frequency, but ...
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, ...

### Sound absorption coefficients for frequencies higher than 8kHz and lower than 80Hz?

The main reason why the tables don't have it, is that it's hard to measure. The measurement technique in ISO 354:2003 relies on measuring the difference in reverberation times in a reverberation rooms ...
Accepted

### How to change speed of audio samples without changing pitch?

This question (about "time-scaling" audio) is closely related to pitch shifting, which is time-scaling combined with resampling. But changing the speed without changing pitch is only time-scaling, so ...
Accepted

### Can I have some feedback on this research paper?

Comments provided here are in two broad categories: Presentation and Subject matter. The "Presentation" section is the easiest to address. There are some things that could be rephrased in terms of ...

### Is sound the best way to transmit a signal under water?

Yes, actually sound waves are better than RF signal in underwater, because of the low frequency requirement. We don't covert sound waves to radio signals. The transceiver in this case is called ...
Accepted

### MUSIC Algorithm for Direction of Arrival (DOA) in Acoustic Signals

The steering vector basically applies the delay according to the spatial location of the Uniform Linear Array (ULA). The multiplication by the complex exponential basically applies the delay. The ...
Accepted

### MUSIC implementation in Pyroomacoustics library

Why the Code Works It's important to note that the MUSIC algorithm works on the microphone array dimension only. So it doesn't care how the data on the receive channels (microphones in this case) has ...

### Random Peak at the end Impulse Response

I would agree on Hilmar's comment, it's probably harmonics generated by nonlinearities of the system in combination with how the logarithmic frequency sweep response is deconvolved into an impulse ...

### Is sound the best way to transmit a signal under water?

You have 3 ways of communicating underwater 1) Acoustic : Most popular means of communication. Has high latency but good range 2) Low frequency RF. To increase the range you have to lower the ...

### Is sound the best way to transmit a signal under water?

The best way for underwater communication is to be acoustic communication where sound waves are used. Sometimes, visible light is used such as red and green, but in all cases, acoustic communication ...

### Phase Difference Calculation in Frequency Domain

SIMPLE 2 BIN SOLUTION FOR FREQUENCY AND PHASE - BOTTOM LINE The following is the summary for the 2 bin solution to determine the exact frequency and phase given the largest DFT bin and the next ...
Accepted

### What additional inputs are required to convert dBFS to dB SPL?

Intro As already stated in another answer, this is not an easy task to perform when your setup is complex (comprised of many discrete apparatus pieces), as each piece must be included in the process, ...

### How to extract pressure values from a WAVE file?

I would be sceptical about prosumer hardware having reliable absolute level reproduction. Is it not safer to record a reference signal (in air acoustics you would have a reference sound source that ...
Accepted

### What is the difference between undersampling and oversampling in analog to digital conversion ?

Good question as you can actually undersample and oversample at the same time! See my "DSP Puzzle" question on that specifically here: How do you simultaneously undersample and oversample? To best ...

### What additional inputs are required to convert dBFS to dB SPL?

What is missing needed for the conversion? You need to identify the entire signal chain of your specific setup. This typically includes at least the microphone, pre-amplifier, ADC input stage, and ...
Accepted

### Is Phase Locked Loop is essential for BPSK signal reception?

There are three different kinds of synchronization in a passband digital communications system: Carrier synchronization: the receiver needs to know the exact frequency and phase of the carrier used ...
Accepted

### Using all-pole filter to model the Room Impulse Response

It's not because of reverberation. When you want to model the Frequency Response of the room, it's common to simplify your approximation by using either all-pole or all-zero models. You don't want to ...
Accepted

### Double the "speed", double the frequency?

White noise: sounds exactly the same if you play it back at double the speed Stack up diminished fifth starting at a low enough fundamental (say 20 Hz). Play back at double speed: sounds exactly the ...

### Convolving Room Impulse Response with a Wav File (python)

It is a little late, but i'm also working on convolution reverb at the moment. If it is still of interest, you can use my code. Simply call the function convolution_reverb and pass the paths to the ...
Accepted

### How many samples per cycle(time period) is actually enough to reproduce the sine wave sound properly?

It depends on how good your interpolation between samples is. If you have really good interpolation, anything more than 2 samples per cycle will suffice. This is not just a theoretical fact, it is ...

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

To a first approximation, a plucked string has an exponential decay, so your envelope will look like $$x(t) = a \exp -bt.$$ The physical explanation for this is simple: when you pluck the string, you ...
Accepted

### What are the limitations of using Magnetic induction rather than acoustic communication in underwater communication

Actually, magnetic induction is a current research topic for underwater communications, see http://bwn.ece.gatech.edu/papers/2015/j14.pdf. Also, this paper includes a nice comparison of underwater ...

### RMS level from impulse response

Please refer to Parseval's theorem. If your impulse response is $h(n)$ and its DFT is $H(k)$, then $$\sum_{n=0}^{N-1} |h(n)|^2 = \frac{1}{N} \sum_{k=0}^{N-1} |H(k)|^2$$ So the square root of the sum ...
Let's look at a simple block diagram The microphone receives the input sound but also reproduced sound from the loudspeaker. There are two transfer functions in place. One, $A(\omega)$ from the ...