Frequency drift in Core Audio on OSX -


i have skeleton audio app uses kaudiounitsubtype_haloutput play audio via aurendercallback. i'm generating simple pure tone test things out, tone changes pitch noticeably time time; drifting or down, , changing rapidly. can couple of tones out @ ~500hz. here's callback:

static osstatus outputcallback(void *inrefcon, audiounitrenderactionflags *ioactionflags,                                const audiotimestamp *intimestamp, uint32 inoutputbusnumber,                                uint32 innumberframes, audiobufferlist *iodata) {      static const float frequency = 1000;     static const float rate = 48000;     static float phase = 0;      sint16 *buffer = (sint16 *)iodata->mbuffers[0].mdata;      (int s = 0; s < innumberframes; s++) {         buffer[s] = (sint16)(sinf(phase) * int16_max);         phase += 2.0 * m_pi * frequency / rate;     }      return noerr;  }

i understand audio devices drift on time (especially cheap ones built-in io), a lot of drift — it's unusable music. ideas?

recording http://files.danhalliday.com/stackoverflow/audio.png

you're never resetting phase, value increase indefinitely. since it's stored in floating-point type, precision of stored value degraded value increases. cause of frequency variations you're describing.

adding following lines body of for() loop should mitigate problem:

if (phase > 2.0 * m_pi)     phase -= 2.0 * m_pi;

changing type of phase float double significantly.


Comments

Post a Comment

Popular posts from this blog

java - Spring Data JPA: Why findOne(id) executing delete query internally? -

i have 1 application using @manytomany annotation link 2 different entities 1 parent entity. not sure if have implemented properly. when execute .findone() on parent entity's repository find it, @ first fetch data along executing delete queries internally delete record mapping table (a table jpa creates after adding @manytomany annotation.). following generated sql queries , code snippet: java class @entity @table(name = "inventory") public class inventory { @id long id; // many other properties @manytomany(fetch=fetchtype.lazy) private list<stream> streams; @manytomany(fetch=fetchtype.lazy) private list<subject> subjects; } there no other annotation i've put in stream , subject entity class link inventory class. when run app, create following tables: inventory stream subject inventory_stream inventory_subject (inventory_stream , inventory_subject, 2 tables created automatically, don't k...
Read more

python - Mongodb How to add addtional information when aggregating? -

i beginner , wrote line pipeline works, wanna add other information output, screen name , or number of tweets.i tried add under $group gave me syntax error everytime here pipeline: def make_pipeline(): # complete aggregation pipeline pipeline = [ { '$match': { "user.statuses_count": {"$gt":99 }, "user.time_zone": "brasilia" } }, { "$group": { "_id": "$user.id", "followers": { "$max": "$user.followers_count" } } }, { "$sort": { "followers": -1 } }, { "$limit" : 1 } ]; i using on example : { "_id" : objectid("5304e2e3cc9e684aa98bef97"), "text" : "first week of school on :p", "in_reply_to_status_id" : null, "retweet_count" : null, ...
Read more

java - Incorrect order of records in M-M relationship in hibernate -

Image
i have 4 records in bridge table in mysql database. using @manytomany in hibernate, accurate order of employees incorrect incorrect of projects. following required material figure out doing mistake. this source. @entity @table(name="project") public class projectbean { @id @generatedvalue @column(name="project_id") private int projectid; @column(name="title") private string projecttitle; @manytomany(mappedby="projects") private collection<employeebean> employees; public projectbean() { employees = new arraylist<employeebean>(); } //getters & setters } @entity @table(name="employee") public class employeebean { @id @generatedvalue @column(name="employee_id") private int employee_id; @column(name="first_name") private string ...
Read more