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  • Visualizing volume of PCM samples

    - by genevincent
    I have several chunks of PCM audio (G.711) in my C++ application. I would like to visualize the different audio volume in each of these chunks. My first attempt was to calculate the average of the sample values for each chunk and use that as an a volume indicator, but this doesn't work well. I do get 0 for chunks with silence and differing values for chunks with audio, but the values only differ slighly and don't seem to resemble the actual volume. What would be a better algorithem calculate the volume ? I hear G.711 audio is logarithmic PCM. How should I take that into account ?

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  • When is calculating or variable-reading faster?

    - by Andreas Hornig
    hi, to be honest, I don't really know what the "small green men" in my cpu and compiler do, so I sometimes would like to know :). Currently I would like to know what's faster, so that I can design my code in a more efficient way. So for example I want to calclate something at different points in my sourcecode, when will it be faster to calculate it once and store it in a variable that's read and used for the next points it's needed and when is it faster to calculate it everytime? I think it's depending on how "complex" and "long" the calculation is and how fast then cache is, where variables are stored, but I don't have any clue what's faster :). Thanks for any reply to my tiny but important question! Andreas PS: perhaps it's important to know that I code in JAVA, but it's more a genral question.

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  • Comparing (similar) images with Python/PIL

    - by Attila Oláh
    I'm trying to calculate the similarity (read: Levenshtein distance) of two images, using Python 2.6 and PIL. I plan to use the python-levenshtein library for fast comparison. Main question: What is a good strategy for comparing images? My idea is something like: Convert to RGB (transparent - white) (or maybe convert to monochrome?) Scale up the smaller one to the larger one's size Convert each channel (= the only channel, if converted to monochrome) to a sequence (item value = color value of the pixel) Calculate the Levenshtein distance between the two sequences Of course, this will not handle cases like mirrored images, cropped images, etc. But for basic comparison, this should be useful. Is there a better strategy documented somewhere?

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  • Effective file permissions tool's api in windows

    - by apoorv020
    Starting from Windows Server 2003, Windows included a new tool which calculates the effective permissions for a user (basically it resolves all groups access and takes care of all "deny" permissions as well). An example in point is that a user A belongs to groups B and C. B has been denied read permissions on a file F, while C has been allowed read and write permissions on the file and I want to calculate the effective permissions user A has on file F. This tool is available on Windows Server 2003,Vista,7 and Server 2008 by right clicking on a file and going to properties - security - advanced - effective permissions. What I need is an API in C# which does the same job. The most common FILE API returns access rules (class FileAccessRules), but there seems to be no direct way to calculate effective permissions from these set of access rules. Note: I do not want to process effective permissions in the code if at all possible, but am ready to do so as a last resort.

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  • Sparse O(1) array with indices being consecutive products

    - by Kos
    Hello, I'd like to pre-calculate an array of values of some unary function f. I know that I'll only need the values for f(x) where x is of the form of a*b, where both a and b are integers in range 0..N. The obvious time-optimized choice is just to make an array of size N*N and just pre-calculate just the elements which I'm going to read later. For f(a*b), I'd just check and set tab[a*b]. This is the fastest method possible - however, this is going to take a lot of space as there are lots of indices in this array (starting with N+1) which will never by touched. Another solution is to make a simple tree map... but this slows down the lookup itself very heavily by introducing lots of branches. No. I wonder - is there any solution to make such an array less sparse and smaller, but still quick branchless O(1) in lookup?

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  • point light illumination using Phong model

    - by Myx
    Hello: I wish to render a scene that contains one box and a point light source using the Phong illumination scheme. The following are the relevant code snippets for my calculation: R3Rgb Phong(R3Scene *scene, R3Ray *ray, R3Intersection *intersection) { R3Rgb radiance; if(intersection->hit == 0) { radiance = scene->background; return radiance; } ... // obtain ambient term ... // this is zero for my test // obtain emissive term ... // this is also zero for my test // for each light in the scene, obtain calculate the diffuse and specular terms R3Rgb intensity_diffuse(0,0,0,1); R3Rgb intensity_specular(0,0,0,1); for(unsigned int i = 0; i < scene->lights.size(); i++) { R3Light *light = scene->Light(i); R3Rgb light_color = LightIntensity(scene->Light(i), intersection->position); R3Vector light_vector = -LightDirection(scene->Light(i), intersection->position); // check if the light is "behind" the surface normal if(normal.Dot(light_vector)<=0) continue; // calculate diffuse reflection if(!Kd.IsBlack()) intensity_diffuse += Kd*normal.Dot(light_vector)*light_color; if(Ks.IsBlack()) continue; // calculate specular reflection ... // this I believe to be irrelevant for the particular test I'm doing } radiance = intensity_diffuse; return radiance; } R3Rgb LightIntensity(R3Light *light, R3Point position) { R3Rgb light_intensity; double distance; double denominator; if(light->type != R3_DIRECTIONAL_LIGHT) { distance = (position-light->position).Length(); denominator = light->constant_attenuation + (light->linear_attenuation*distance) + (light->quadratic_attenuation*distance*distance); } switch(light->type) { ... case R3_POINT_LIGHT: light_intensity = light->color/denominator; break; ... } return light_intensity; } R3Vector LightDirection(R3Light *light, R3Point position) { R3Vector light_direction; switch(light->type) { ... case R3_POINT_LIGHT: light_direction = position - light->position; break; ... } light_direction.Normalize(); return light_direction; } I believe that the error must be somewhere in either LightDirection(...) or LightIntensity(...) functions because when I run my code using a directional light source, I obtain the desired rendered image (thus this leads me to believe that the Phong illumination equation is correct). Also, in Phong(...), when I computed the intensity_diffuse and while debugging, I divided light_color by 10, I was obtaining a resulting image that looked more like what I need. Am I calculating the light_color correctly? Thanks.

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  • Converting from samplerate/cutoff frequency to pi-radians/sample in a discrete time sampled IIR filter system.

    - by Fake Name
    I am working on doing some digital filter work using Python and Numpy/Scipy. I'm using scipy.signal.iirdesign to generate my filter coefficents, but it requires the filter passband coefficents in a format I am not familiar with wp, ws : float Passband and stopband edge frequencies, normalized from 0 to 1 (1 corresponds to pi radians / sample). For example: Lowpass: wp = 0.2, ws = 0.3 Highpass: wp = 0.3, ws = 0.2 (from here) I'm not familiar with digital filters (I'm coming from a hardware design background). In an analog context, I would determine the desired slope and the 3db down point, and calculate component values from that. In this context, how do I take a known sample rate, a desired corner frequency, and a desired rolloff, and calculate the wp, ws values from that? (This might be more appropriate for math.stackexchange. I'm not sure)

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  • Lucene numDocs and doqFreq on custom similarity class

    - by David A
    Hi All, im doing an aplication with Lucene (im a noob with it) and im facing some problems. My aplication uses the Lucene 2.4.0 library with a custom similaraty implementation (the jar is imported) In my app im calculating doqFreq and numDocs manually (im adding the values of all indexes and then i calculate a global value in order to use it on every query) and i want to use that values on a custom similarity implementation in order to calculate a new IDF. The problem is that I dont know how to use (or send) the new doqFreq and numDocs values from my app on that new similarty implementation as I dont want to change lucene´s code apart from this extra class. Any suggestions or examples? I read the docs but i dont now how to aproach this :s Thanks

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  • Python lazy property decorator

    - by detly
    Recently I've gone through an existing code base and refactored a lot of instance attributes to be lazy, ie. not be initialised in the constructor but only upon first read. These attributes do not change over the lifetime of the instance, but they're a real bottleneck to calculate that first time and only really accessed for special cases. I find myself typing the following snippet of code over and over again for various attributes across various classes: class testA(object): def __init__(self): self._a = None self._b = None @property def a(self): if self._a is None: # Calculate the attribute now self._a = 7 return self._a @property def b(self): #etc Is there an existing decorator to do this already in Python that I'm simply unaware of? Or, is there a reasonably simple way to define a decorator that does this? I'm working under Python 2.5, but 2.6 answers might still be interesting if they are significantly different.

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  • Javascript/jQuery height calculation

    - by danit
    Im looking for a way, in javascript, to calculate the size of the browser (px) then calculate the size of a <div> taking away 50px from that full screen size: E.g. Browser screen size: 800px (Height) Existing <div> that is always 50px (Height) Leaves 750px (Height) for the remaining <div> to fill the page. Then take that 750px and apply it as inline style: <div style="height: 50px"> <img src="banner.png" /> </div> <div style="height: x"> This fills the remainder of the page </div>

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  • Java Future and infinite computation

    - by Chris
    I'm trying to optimize an (infinite) computation algorithm. I have an infinte Sum to calculate ( Summ_{n- infinity} (....) ) My idea was to create several threads using the Future < construct, then combine the intermediate results together. My problem hoewer is that I need a certain precision. So I need to constantly calculate the current result while other threads keep calculating. My question is: Is there some sort of result queue where each finished thread can put its results in, while a main thread can receive those results and then either lets the computation continues or terminate the whole ExecutorService? Any Help would really be appreciated! Thanks!

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  • Audio -- How much performance improvement can I expect from from reducing function calls by using bu

    - by morgancodes
    I'm working on an audio-intensive app for the iPhone. I'm currently calling a number of different functions for each sample I need to calculate. For example, I have an envelope class. When I calculate a sample, I do something like: sampleValue = oscilator->tic() * envelope->tic(); But I could also do something like: for(int i = 0; i < bufferLength; i++){ buffer[i] = oscilatorBuffer[i] * evelopeBuffer[i]; } I know the second will be more efficient, but don't know by how much. Are function calls expensive enough that I'd be crazy not to use buffers if I care event a tiny bit about performance?

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  • Get the distance between two geo points

    - by Chmouel Boudjnah
    Hi, I want to make a apps that check what's the nearest place from where the user is. I can easily get the location of the user and I have a list of places with latitude and longitude. What would be the best way to know the nearest place of the list against the current position. I could not find anything in the google APIs. I am worried I need to resort to my calculate and have to do math to calculate it. What do you guys think ? Cheers and thanks for reading or replying.

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  • Methods for content uniqueness calculation on C#

    - by sashaeve
    I have a set of text files. I want to calculate a content uniqueness for different subsets. E.g. we have 10 documents (A1 - A10) and want to calculate the uniqueness for subset of documents A1 and A2. So the result must be some value from 0 to 1 (1 - absolutely unique content, 0 - absolutely dublicated content). What methods for content uniqueness calculation do you know? Please suggest these methods with .NET implementations. Thanks.

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  • Programming user interface advice?

    - by onurozcelik
    Hi, In my project I going to generate a user interface through programming. Scalability of this UI is very important requirement. So far I am using two dimensional graphics for generating the UI. I think there may be different solutions but for the moment I know only two. First one is supplying X,Y coordinates of each two dimensional graphic on my UI.(I do not prefer this solution because I do not want to calculate X,Y coordinates of each graphic. For the moment I don't have a logic for doing this easily) Second one(which is currently I am using now) is using layouts which organizes its contents according to size of item. In this solution I don't have to calculate X,Y coordinates of each item.(Layout is doing this for me) But this approach may have its own pitfalls. I am very new to user interface programming. Can you give me advice about this issue?

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  • Position text in top of a dinamically generated map area of type poly

    - by Guillermo Vasconcelos
    Hi, I have a web page with a dynamically generated image map (from a server side charting tool that I have no control over). I have a value for each area in the title attribute that I want to display on top of the image. I could dynamically generate span elements with absolute positioning, but I'm not sure how to calculate the "center" of a poly shaped area to use as coordinates. Is there an easy way to create texts for image map areas? a JQuery plug in perhaps? Do you know a good way to calculate the center of a poly area? Do you have any other suggestions? Thanks, Guillermo

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  • Google maps nearest points avoiding rivers / by itinerary

    - by Karl Lacroix
    Here is the deal : I need to find the closest points from a point with a radius. For example, I need to get all the points in a 15 km radius. Thats easy with Google Maps Radius and all the examples on the web ;) The problem is that from my office, a point is under the 15km radius, but it's on the other side of a river, so the car itinerary is about 30 km (using a bridge)! Is there a simple solution to exclude those points or to calculate by intineraries ? I supposed that I'll need to calculate all itineraries with returned points? DirectionsRequest API? Thanks! :)

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  • Calculating usage of localStorage space

    - by WmasterJ
    I am creating an app using the Bespin editor and HTML5's localStorage. It stores all files locally and helps with grammar, uses JSLint and some other parsers for CSS and HTML to aid the user. I want to calculate how much of the localStorage limit has been used and how much there actually is. Is this possible today? I was thinking for not to simply calculate the bits that are stored. But then again I'm not sure what more is there that I can't measure myself.

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  • code to edit the text in an EditText widgit

    - by user293663
    Hello, I am a newbi programmer and am having trouble with a measurement conversion program I am working on. What I would like to do is have several EditText boxes. When one is filled in and a calculate button is hit then the rest will be populated with a converted number. The part I am getting stuck on is outputting the answers to EditText widgets. ex: There are three EditText Widgets. a user inputs the number 6 into the first one (labeled inches) and presses calculate. I would like the next box to display .5 (labeled feet) and the last to display .1666 (this would be yards) .setText() apparently does not work to modify the text in an EditText any help would be greatly appreciated.

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  • Binomial test in Python

    - by Morlock
    I need to do a binomial test in Python that allows calculation for 'n' numbers of the order of 10000. I have implemented a quick binomial_test function using scipy.misc.comb, however, it is pretty much limited around n = 1000, I guess because it reaches the biggest representable number while computing factorials or the combinatorial itself. Here is my function: from scipy.misc import comb def binomial_test(n, k): """Calculate binomial probability """ p = comb(n, k) * 0.5**k * 0.5**(n-k) return p How could I use a native python (or numpy, scipy...) function in order to calculate that binomial probability? If possible, I need scipy 0.7.2 compatible code. Many thanks!

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  • Determine Click-thru Percentage With PHP

    - by Lea
    Hi all, I am currently working on a small sponsorship application(PHP/MySql) for my personal blog, and am almost finish, but I am stuck on how to calculate the click-thru rate of my sponsors campaigns. I was always terrible with working out percentages, so any practical help would be appreciated. The data is stored in the DB as simple numbers.. So as expected, when a page refreshes, or a sponsors ad is clicked, the data updates with an incrementation of 1. So using these values...say $clicks and $impressions, how would I determine the click-thru rate? What would be the sum I would use to calculate? An example function would really be appreciated. Kind Regards, Lea

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  • Need a formula for calculating the tax portion of a total amount.

    - by pawz
    In Australia we have to advertise products with tax already added, so rather than say a product is $10 + $1 GST = $11, we normally work backwards and say "ok, total is $10, how much of that is GST ?" For example, for a $10 total, you do 10 * (1 /11) = 0.91, which is the tax component of the $10 total. My problem is I need calculate a formula for working out the taxable component when the tax rate is a variable. So far I've made this calculation although I'm not sure how correct an assertion it is: 10 * (1 / x) = 0.09 * (1 / y) where y = 10, x = 11 Basically i want to work out x on the left hand side when I know that the tax rate is 0.05 for example, which will give me a formula that I can use to calculate the taxable component of an total figure. I want a function into which I can plug in the total price and the tax rate, and get back the taxable component of the total price. I'd really appreciate the help with this as it really makes my head hurt ! :")

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