Questions tagged [fixed-point]
The fixed-point tag has no usage guidance.
83
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Fixed point implementation of IIR filter
I am trying to implement an IIR filter followed by downsampler with the following specifications:
fs=18000,order=8,3db freq=[500 1000],downsampling factor=6.
...
- 161
4
votes
4
answers
846
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Fixed point scaling; float -> Q31 -> float
I am new to DSP and I am trying to understand how to work with fixed point operations and in particular the Q31 format.
In floating point (full range) I am doing some multiplications, it could be for ...
- 158
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2
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71
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Fixed point restrictions with respect to DSP
I assume that fixed-point arithmetic can handle most of the traditional linear DSP tasks. As far as I know, there is a restriction for the FFT length with respect to the fixed point bit-depth.
Is ...
2
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1
answer
182
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Fixed-Point Filter Design: Where comes the DC-Gain difference between the bode plot and the step response from?
Introduction: What I wanted to achieve
I am currently trying to implement a digital fixed-point filter on a STM32-Microcontroller by using the ARM CMSIS-DSP Library Link to reference manual.
The ...
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1
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212
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Calculate the Gain of a fixed-point filter
As the title already says, I would like to know how to calculate the Gain and Phase of a given fixed-point filter at a given frequency.
What I've achieved so far:
Let's say for example that I have a ...
- 25
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1
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161
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How to apply hann window to unsigned integer ADC
I am using Arm-Cortex M3 Microcontroller and CMSIS for FFT, my microcontroller does not support floating point unit therefore I have to use fixed point (Q15 or Q31) for calculation.
Before calculate ...
- 13
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1
answer
41
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Evaluating the accuracy of an integrator
I'm designing a digital signal processing chain that includes integration of a periodic input followed by decimation/resampling. The processor is integer/fixed point only, so the primary source of ...
- 55
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2
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220
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best way to converting data from uint16_t to q15 for least saturation error
Q15 standard is fixed point fraction from -1 to 1 represented by 15 bit, and uint16 is numbers from 0 to 2¹⁶.
I have data range from 0 to 2¹², I can directly cast them to Q15 and all the data will ...
- 315
1
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2
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164
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Integer v Fractional ADC outputs with FIR Filter Inputs
I have a system I'm working on that inputs an 18 bit ADC output into an FIR filter on a Xilinx FPGA. I'm a little concerned I may be representing the numbers wrong. My ADC outputs a signed 18-bit ...
- 266
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1
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214
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Modelling and testing fixed point IIR filter with freeware tools
I understand from this other question that prior to implementing a fixed point IIR filter on a particular microcontroller target it's best to create a model using a DSP tool and compare the output to ...
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178
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How can we correctly use the CMSIS-DSP functions that have fixed-point (Qx) input/outputs?
I want to use Arm CMSIS-DSP library functions to perform matrix-vector multiplications on integers. It seems that the library, instead of integers, mainly supports operations on fixed-point numbers in ...
- 113
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322
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Wrong result when realizing fixed-point biquad IIR filter
I'm implementing a fixed-point direct form I biquad filter with Q1.15 precision. I use fraction saving to improve quantization error. However, my function gives me the different results compared by ...
- 485
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3
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526
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Why does the Direct form I become our first choice for fixed-point implementation?
I heard that the Direct form II transposed is better for floating-point and the Direct form I is better for fixed-point. Is it true?
I understand that DF2 and DF1T should never be used in fixed-point ...
- 2,855
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2
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52
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Why we sometime use some values of fixed point and floating point both in dsp?
I have been writing kernels for a communication dsp device, which uses cmac/cmad operation on fixed and floating point numbers. I am not very clear why both types is used in the same operation.
- 11
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1
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505
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Fixed point saturation and round
Another question related to fixed point saturation and rounding. Say using notation S<WL, FW> where S means it is signed number, WL is the full bitwidth, and FW is the fractional bitwidth. So S&...
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3
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500
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Implementation of CIC filter using floating point
I am trying to implement a CIC filter and was reading through the literature and found that CIC filter cannot be implemented using floating point. I am unable to understand why that would happen. The ...
- 41
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2
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113
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DSP signal filtering and number formats
I'm working on a dsPIC33, using Audio Codec Board - Proto to read audio samples and for reproduction.
In order to implement a relatively simple signal processing algorithm, I'm reading audio samples ...
3
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2
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371
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High-pass filter with quantized (fixed-point) coefficients
I have a high pass IIR filter with numerator
b = [0.997688673703782,-1.995377347407564,0.997688673703782];
and denominator
...
- 2,855
2
votes
1
answer
94
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State-space filters in fixed-point?
I am having difficulties implementing state-space filters in (32-bit) fixed-point. This is because the coefficients have a huge dynamic range, for example (MATLAB code):
...
- 492
2
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1
answer
164
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How to evaluate fixed-point implementation of LMS filter is correct?
I am having an LMS block with 6 filter coefficients.
The value of filter coefficients are
0.0001
0.00045
0.2535
0.546536
0.0000243
0.3423
I have tried to ...
- 161
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0
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50
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Efficient way to calculate eigen-values of a 2x2 matrix
I'm working on an algorithm that works based on finding the eigen-values of a 2x2 complex covariance matrix. However, from a fixed-point implementation point of view, finding eigen-value of a matrix ...
- 101
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0
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128
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Strange behavior in fixed-point FFT
This is a problem I encountered some time ago while doing my thesis, which still now, I am not sure to understand.
By then, I was implementing the circular correlation in an FPGA using this Xilinx FFT ...
- 76
1
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1
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50
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signed 2's complement of a negative number for Integer = 3 and Fraction = 9
I am working on signed 2's complement for my fractions coefficients. Below code can be used for positive inputs. However for a negative 2's complement when I added LSB with 1, then an error pops. I ...
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43
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Are there any tools for generating fixed point filter implementations?
It's very easy to make a filter in Scipy or many other tools, but implementing this filter in fixed point in C or VHDL/Verilog is always a chore. I mean, in theory it's just a matter of adequately ...
- 248
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79
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Problem with natural logarithmic function in fixed point notation
I am facing a problem with natural logarithmic function in fixed-point notation.
Let's say
$$x = 0.54, \qquad\text{then}\qquad \ln(x) = -0.616186, \qquad\text{a negative number} \tag{1}$$
Then in ...
- 59
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34
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Changing Coherence function from float to fixed point
I want to calculate the coherence between two audio signals. After referring a few websites, I found that the coherence is calculated by using the equation $(1)$ which is as follows
$$\rm Coherence = \...
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2
votes
1
answer
116
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Clear examples of Fixed Point Algorithm Specification Block Diagram for FPGA Implementer
I have been working on converting a simple, floating point algorithm to fixed point and need to create a block diagram to help the guy who will implement this on an FPGA. As often is the case, the ...
- 375
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1
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175
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How to improve accuracy while converting floating point coefficients to fixed point in the case of an all pole IIR filter
I am having an all pole IIR filter of order 5 with floating point filter coefficients
...
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1
answer
324
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Friendliest python library for fixed point algorithm simulation
My primary programming language is python. Is anyone aware of solid python libraries to simulate fixed point algorithms in python? A quick google search revealed this:
https://pypi.org/project/...
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2
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104
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Fixed Point Design Resources
Can anyone point me to good methodologies for designing fixed point versions of possibly nonlinear signal processing algorithms?
Are there any systematic methods other than simulation for optimizing ...
- 375
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5
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2k
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Single pole IIR filter, fixed point design
We want to do a fixed point implementation of the single pole IIR filter:
$y[n] = a\cdot x[n] + (1 - a)\cdot y[n-1] \quad ;\qquad 0<a<1$
What are the main design considerations to think about ?...
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1
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78
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How to specify the input data bit width for fixed point implementation in windowed OFDM?
I am implementing a fixed point model of Windowed OFDM and to quantize the input data, I used 16 bits(complex) to encode it. But I am not sure how do we specify the minimum number of bits that should ...
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7
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3k
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Why is there no FPU on (most) DSP chips?
Why is there no FPU (Floating Point Unit) on most DSP chips? I found
several answers such as this
one
that explain advantages of fixed point approach such as smaller power
consumption, higher speed ...
- 169
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2
answers
295
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FFT error when number of samples growth - Matlab/octave
I see when I increase number of samples, the imaginary error part of the FFT growth due to the error of sin(n*pi)!=0 where n is the index of the sample in Matlab or octave.
Is there anyway to force ...
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22
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What is the meaning of these Fixed Point Properties e.g.CustomSectionInputDataType?
I was trying tom implement a Butterworth filter and i came across a example on Mathworks site which emphasizes to customize various terms related to the filter.
Following are some of the terms i could ...
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1
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287
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Methods to evaluate the quality of an IIR Filter fixed-point implementation
I'm implementing a scattered look-ahead IIR filter in Matlab/VHDL, basically I convert an order-2 IIR filter into an order-4 IIR in order to take advantage of the pipelining of an FPGA. (reference ...
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33
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CoeffFracLength negative or larger than the CoeffWordLength [Fixed-Point Filter Properties in Matlab]
I have been reading the fixed-point filter properties in Matlab and I have found that the parameter "CoeffFracLength" can be either zero, negative or positive. And also, it can be larger than the ...
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2
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390
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Floating point to fixed point in C
I've been trying to make a digital filter.
I've used the following transfer function to get my digital coefficients
https://gyazo.com/00195ef119f0b2ff93fa5855715abdc9
Which i've then transfered to ...
0
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2
answers
159
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Hyperbolic sine "sinh" in fixed-point?
As part of an audio peaking filter calculation, I need to implement hyperbolic sine ("sinh") function in a fixed-point arithmetic (fixed-point DSP processor).
What is the proper way to do this?
- 492
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2
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802
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Conversion from Floating point representation to Fixed point representation
I have written a matlab function for a constellation mapper and I want to create a Fixed-point version of that code for implementation on FPGA. I know matlab has a specific toolbox for fixed-point ...
- 13
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0
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69
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How to calculate the magnitude of rounding error in N-bit signed fixed-point arithmetic?
In example take into consideration 11-bit <11,5> signed fixed-point arithmetic.
000000.11111 - 0.96875
000001.00000 - 1
so the error magnitude will ...
- 227
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1
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256
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VHDL fixed point implementation of IIR filter
I have a filter described by the following transfer function H(z):
$$H(z) = \frac{156 - 156z^{-2}}{16384 - 32443z^{-1}+16073z^{-2}}$$
How will this be implemented with the first term in the ...
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2
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99
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Audio Bit Depth "mapping" from DAW to Audio card: is this correct?
Let say I'm generating a 1 kHz sine wave within my DAW, using some synth (Sytrus in my case). I normalize it, so it play at max "digital" amplitude 0db.
Thus, any sample of the signal would gets a ...
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1
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853
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What is the correct way to handle Saturation on a DSP?
Let's say I have 16 bit fixed point DSP, and am performing a multiply accumulate operation in a loop-
What would be the correct way to check for saturation of the accumulated value? As far as I ...
- 53
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1
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547
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How to convert floating point code to fixed point?
I am working on converting a floating point MATLAB code into fixed point C code. The code is to be run on a DSP platform, the specifics of which are yet to be decided.
I'm new to floating point to ...
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1
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853
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Multiplication of fixed-point numbers
I'm trying to understand the professor who wrote about Q2-fixed-point number 1.01 and 1.11 which should be multiplied. I don't understand anything.
Multiply the Q2-fixed-point number 1.01 and ...
1
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1
answer
66
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Is it necessary to scale a signal for quantization noise analysis?
I am doing a series of tests to analyse the round-off (quantization) noise performance of single and two stage biquad cascades (direct form 1), at different sampling rates. The system I am simulating ...
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312
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Fixed point Error Spectrum Shaping (noise shaping) for biquads
Based on that article and all the resources on the internet that advise the use of noise shaping for fixed-point filter implementations, I tried to make a few simulations on Matlab for the biquad I'm ...
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482
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Converting floating point IIR to fixed point arithmetic, given its difference equation
Is there some general way to perform the task given in the question? I have a filter given as follows:
...
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2
answers
1k
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Trouble with fixed-point arithmetic 2nd order IIR implementation in c
DSP newcomer here!
I am tinkering around with a TI DSP and am trying to implement a second order IIR filter in C. Input is 16 bit 2's complement, as is the output, the accumulator is 32 bit wide.
I ...
