Questions tagged [fixed-point]

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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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31 views

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
1 vote
94 views

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
28 views

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 ...
1 vote
50 views

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 ...
1 vote
70 views

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 ...
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45 views

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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1 vote
37 views

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
154 views

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 ...
• 169
248 views

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 ...
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43 views

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.
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231 views

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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304 views

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 ...
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83 views

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 ...
252 views

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 ...
• 2,330
83 views

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): ...
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1 vote
122 views

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 ...
• 93
36 views

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
103 views

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 ...
1 vote
45 views

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 ...
• 13
35 views

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 ...
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1 vote
76 views

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 ...
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1 vote
86 views

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 ...
• 213
780 views

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 ...
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1 vote
523 views

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 ...
809 views

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 vote
60 views

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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1 vote
273 views

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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1 vote
454 views

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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1k views

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 ...
267 views

Optimization of Filter Coefficients to Given Word Length

It seems to me that this is a difficult mathematical problem where research is still carried on: Is there an efficient way to find fixed-point coefficients whose zeros are closest to those calculated ...
1 vote
112 views

Implementation of IIR Filter in dsPIC 33EP - Q15

I am implementing an IIR controller in dsPIC 33EP (16-bit, fixed-point, two's complement, wrap-around, 40-bit accumulator, 32-bit multiply, 12-bit ADC) and I am using cascaded, Direct Form I second ...
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I'm trying to implement a band-stop (notch) filter on a microcontroller dsPIC33EP64GS506 to filter out a $100\textrm{ Hz}$ component from an input signal. The ...