# Questions tagged [fixed-point]

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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
846 views

### 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
1 vote
71 views

### 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 ...
182 views

### 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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### 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 ...
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1 vote
161 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
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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 ...
1 vote
220 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
164 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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### 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 ...
• 133
1 vote
178 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
322 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 ...
• 485
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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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### 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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1 vote
505 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&...
• 13
500 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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### 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 ...
371 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 ...
• 2,855
94 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): ...
• 492
164 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 ...
• 161
50 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
128 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
50 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 ...
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43 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 ...
• 248
1 vote
79 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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• 113
1 vote
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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 ...
• 223
853 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 ...
• 53
1 vote
547 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 ...
853 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
66 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 ...
• 11
1 vote
312 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