## Forums More comp.dsp

## Naive question(s) about DTV

inIn the 60's I spent time as a BSEE student. Took a course using _Signals, Systems and Communication_ , Lathi , 1965 A generation later I found...

In the 60's I spent time as a BSEE student. Took a course using _Signals, Systems and Communication_ , Lathi , 1965 A generation later I found comp.dsp and obtained a copy of _Understanding Digital Signal Processing_ , Lyons, 2004 May I answers suitable for a bright high school student who reads eclectically {will account for what I've forgotten &/or never knew ;}. I've a germ of an ide...

## FFT zero analyzing pink noise

inIm doing the pink noise FFT. I calculate the frequency of 1kHz by adding the contribution of the corresponding bins. Is it possible that sometimes...

Im doing the pink noise FFT. I calculate the frequency of 1kHz by adding the contribution of the corresponding bins. Is it possible that sometimes the result is zero? Thanks.

## 5-point stencil or Savitsky-Golay for differences

inI had some code computing the second difference of a sampled signal as (x(n-1)-2x(n)+x(n+1))/(square of interval) I only needed a crude estimate...

I had some code computing the second difference of a sampled signal as (x(n-1)-2x(n)+x(n+1))/(square of interval) I only needed a crude estimate of the second derivative in this case. Then I came across "five point stencils" By this method, the second difference is (-x(n-2)+16x(n-1)-30n(n)+16x(n+1)-x(n+2))/12/(square of interval) And then 5-sample Savitsky-Golay formula, which seems rath...

## Power Ratios?

inI'm confused by some code I wrote to measure signal amplitude from a CODEC. The FPGA sampled for some period of time squaring the samples and...

I'm confused by some code I wrote to measure signal amplitude from a CODEC. The FPGA sampled for some period of time squaring the samples and summing them up. I did not take the square root of the result, at least not in the FPGA. I would expect this result to be proportional to the power in the signal. When I compare this number at multiple frequencies to get the variations,

## Correlation Versus Simple Filter

inGentle Readers, Ok, I've been out of DSP for way too long so maybe this is a stupid question, but in the interest of getting my feet wet...

Gentle Readers, Ok, I've been out of DSP for way too long so maybe this is a stupid question, but in the interest of getting my feet wet again, here goes. Let's say we have a tone which we want to detect. Which is going to give better performance, correlation followed by a threshold or a simple bandpass filter followed by an energy detector and threshold? -- Randy Yates, DSP/Embedded ...

## Ultrasonic speech

inA client for unknown reasons wants to emit speech in teh frequency range above 20kHz. I was wondering what is the best way around this to do a...

A client for unknown reasons wants to emit speech in teh frequency range above 20kHz. I was wondering what is the best way around this to do a frequency shift. Then presumably I would need a sound card on a PC with high sampling rate and ultrasonic amplifier and loudspeaker. (this can be bought). So I sample at say 44.1KHz as usual a section of speech and store to wav file. Then I

## history of coding

inRecently I attended a coding seminar. The speaker very briefly reviewed the relevant history; first Hamming codes, ~1960: BCH codes, ~1970:...

Recently I attended a coding seminar. The speaker very briefly reviewed the relevant history; first Hamming codes, ~1960: BCH codes, ~1970: convolutional, 1995: polar, 2002: LDPC Clue me in - what was the advance in each case? I worked on a BCH project once, that seemed fairly efficient, how is it, or other algorithms, deficient? -- Rich

## Elwyn Berlekamp RIP

inA few of us had the great fortune to work with Elwyn Berlekamp during our careers. He passed away on April 9, 2019. The most prolific and...

A few of us had the great fortune to work with Elwyn Berlekamp during our careers. He passed away on April 9, 2019. The most prolific and most genius expert on algebraic coding, Berlekamp also contributed significantly to game theory, cryptology, and quant. He was a member of the USA National Academies of both Engineering and Science, recipient of both the Shannon Award and the Hamming M...

## Homodyne complex frequency shift

inHi, the input signal is sin(t), I multiply it with cos(t) to get the I component and sin(t) to get the Q component. So...

Hi, the input signal is sin(t), I multiply it with cos(t) to get the I component and sin(t) to get the Q component. So then I(t)=sin(t)*cos(t)=0.5*sin(2t) Q(t)=sin(t)^2 I would expect only the DC component to persist, but instead I have two quickly wiggling waves. What is missing to shift 1kHz to DC without introducing the mirror frequencies? Thanks in advance!

## Multiple PDM mic recording

How to record multiple PDM mics at 16KHz? What is a recommended soundcard/HW that can be used?

How to record multiple PDM mics at 16KHz? What is a recommended soundcard/HW that can be used?

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