Measure dB with AVAudioRecorder is limited to 96dB on iOS -


i'm trying build db measurement unlock feature within app. feature should become available once user reaches 100db. current implementation able measure 96db. understand problem somehow related bitrate recording: 16bit capable of 96db, 24bit should capable of 144db (http://www.head-fi.org/t/415361/24bit-vs-16bit-the-myth-exploded).

the db measurement , calculations work fine, issue can not measure more 96db. i'm struggeling settings achieve higher bit rate, guess i'm doing wrong here.

my current initialisation of recorder looks this:

nsdictionary *settings = [nsdictionary dictionarywithobjectsandkeys:                       [nsnumber numberwithfloat: 44100.0],                 avsampleratekey,                       [nsnumber numberwithint: kaudioformatappleima4],       avformatidkey,                       [nsnumber numberwithint: 1],                         avnumberofchannelskey,                       //[nsnumber numberwithint: 24],                         avencoderbitratekey,                       [nsnumber numberwithint:24],avlinearpcmbitdepthkey,                       [nsnumber numberwithbool:no],avlinearpcmisbigendiankey,                       [nsnumber numberwithbool:no],avlinearpcmisfloatkey,                       [nsnumber numberwithint: avaudioqualitymax],         avencoderaudioqualitykey,                       nil];  nserror *error;  recorder = [[avaudiorecorder alloc] initwithurl:outputfileurl settings:settings error:&error];

thank in advance.

it's important understand db value expression of ratio, not absolute value. in case it's magnitude of signal relative smallest value, 16 bit signed value have 20 * log10(2^16) = 96 db. in other words loudest signal 96 db louder smallest signal. 24 bit data range bigger: 20 * log10(2^24) = 144 db. full scale signal still same value. (note more commonly use full scale reference of 0 db, , express other values negative db values, reference arbitrary).

a common source of confusion when people talk how loud sound is, "db" referring db spl, way of defining loudness relative given reference value (20 µpa (rms)). not confuse db values calculating above, simple ratios, , not directly related loudness.


Comments

Post a Comment

Popular posts from this blog

android - Get AccessToken using signpost OAuth without opening a browser (Two legged Oauth) -

i using signpost oauth access data magento server. have read various tutorials on same , reach point open browser user can enter credentials. however, per requirement have automate part. hence, user should not browser page. have set-up done on server side ( magento ), hit url , returned call page. same through program in android. i have tried below, consumer = new commonshttpoauthconsumer(key, secret); provider = new commonshttpoauthprovider(oauth_init_url,access_token_url, authorize_url); try { provider.retrieverequesttoken(consumer, oauth.out_of_band); log.d("tokens" , consumer.gettoken() + " -- " + consumer.gettokensecret()); } and request tokens. dont know how bypass next step. tried directly accessing accesstoken (stupid of me) provider.retrieveaccesstoken(consumer, "mycallback://callback"); no luck, ends in oauth.signpost.exception.oauthnotauthorizedexception: authorization failed (server replied 401). ...
Read more

org.mockito.exceptions.misusing.InvalidUseOfMatchersException: mockito -

getting error org.mockito.exceptions.misusing.invaliduseofmatchersexception: invalid use of argument matchers! 1 matchers expected, 2 recorded. exception may occur if matchers combined raw values: //incorrect: somemethod(anyobject(), "raw string"); when using matchers, arguments have provided matchers. example: //correct: somemethod(anyobject(), eq("string matcher")); at when( getprogramservice .callservice(any(getprogramtype.class))) .thenreturn(jaxbresponse); please explain error , possible resolution the code posted looks fine; don't see problem it. code before or above causing exception. key here: invalid use of argument matchers! 1 matchers expected, 2 recorded. any , used above, doesn't return "special kind of null" or "special kind of getprogramtype"; don't exist. instead, returns null , side effect puts matcher on stack. whe...
Read more

google shop client API returns 400 bad request error while adding an item -

i'm working on solution add items in google shopping market java application. following tutorial real mess because of missing classes of laste release, after setting 1.5-beta maven managed make base example typecheck correctly classes. still can make simple task of adding 1 item. instead of posting whole code i'm posting part creates product feed. private product createproduct(string id) { product product = new product(); product.title = "red wool sweater"; product.content = new content( "text", "comfortable , soft, sweater keep warm on " + "cold winter nights. red , blue stripes."); product.appcontrol = new appcontrol(); product.appcontrol.addrequireddestination("productads"); product.externalid = id; product.lang = "it"; product.country = "it"; product.condition = "nuovo"; product.price = new price("eu...
Read more