Android Apps - Creating Worf

For the past few months I have been learning the Android development environment and how to create apps for the Google Play store.  My first release is an app called Worf, an advanced audio recorder and spectrum analyzer.  Worf is a great little utility that demonstrates several important concepts of digital signal processing.

For starters, Worf listens to the device's microphone and plots a real-time frequency spectrum.  This alone is not particularly impressive given the number of free spectrum analyzer's already available for Android.  But it was a necessary first step nonetheless to get familiar with audio capture.  There are a number of methods and pre-built libraries floating around for plotting data and whatnot, but I chose to write my own plot routines using the raw Android SDK methods.  It really wasn't that hard and probably easier than trying to learn someone else's library.  I went through a number of different FFT algorithms in both Java and C before settling on a C++ version I really like.  It seems most modern hardware is powerful enough to run any of them in real time, so it's just a matter of personal preference.  I wanted to get familiar with running native C and C++ through JNI anyway, so this was a good excuse.  After performing the FFT and plotting the frequency domain, the data is carted off to a LAME MP3 converter algorithm to render an audio output file.

Next I added a threshold that the user can draw with their finger over top of the audio spectrum.  Amplitude spikes that rise above the threshold anywhere in the spectrum are flagged.  Only the FFT buffers that contain flagged data are actually written to file, the rest are discarded.  After playing around a bit I decided the optimal approach was to capture four sets of data at a time for FFT processing, perform the threshold check on the first and last sets, and then write all four to file if either of the two crossed the threshold.  This provides a little bit of a buffer around the captured audio and helps to prevent things from getting cut off.

Finally, I added a filter that is also drawn in a manner similar to the threshold, but is much much more complicated.  Initially I made the naive mistake of thinking I could filter in the frequency domain by attenuating the data according to the shape of the curve that the user had drawn.  Then an inverse-FFT would yield the filtered time domain data for recording to file.  Well that's not really a good idea.  It sort of works when you get complicated with overlapping FFT's, but the main issue is that the spectrum plot is actually a magnitude, and not the full complex representation of the signal.  Without the imaginary parts it seems the signal quality after attenuation is not very good.

The better method I eventually settled on was to use time-domain filtering.  I chose a Kaiser-Bessel window function (I suppose a variety of others would work as well) to create a band-pass FIR filter.  Then I string together a whole set of FIR filters in parallel centered on each point of the FFT and attenuating the signal by the amount drawn by the user in the filter curve.  Turns out you just need to sum the FIR coefficients, so it's pretty easy and not CPU intensive.  This seems to perform pretty well and doesn't degrade the audio quality (very much).

Depending on the level of interest in this app and these implementation notes, I may post some of the specific algorithms used along with more details in a series of follow up posts.

I am releasing Worf as a free app in the Google Play store later this week.  I just want to do a little more testing with it first to see if there are any hidden bugs remaining.  The link below should work once it is released.

Download Worf from Google Play

Education in America - job salary by field of employment

One of the most sought after but least discussed topics in the workplace is exactly how much a particular position pays on average compared to other jobs in the same or different fields.   Colleges often advertise the value of an education in America in terms of how much more a college graduate can earn versus a high school graduate, but that doesn't really give any specific real world information. The news media loves to publish the occasional "top jobs" list but they are very high level and cursory and intended more as entertainment than reference information.  In previous articles on education in America, the percentage of college graduates by field was presented, as well as the unemployment rate by field.  Here we look at salary and the number of people employed by field.

The U.S. Bureau of Labor Statistics is the only real go-to source for information on jobs, employment, and salaries.  Unfortunately, pulling information out of their database to make meaningful comparisons to was a bit of a chore.  But here it is (click on plots to view full size):

Salary by Job Field, 2009 and 1999

Not surprisingly, management pays the most, followed by law, engineering and healthcare fields.

Number of employees by job field, 2009 and 1999

Evidently there are a ton of office administrative support people out there, but very few cops (protective services).  Finally, the most meaningful chart shows the trends in these professions over the last 10 years.

Salary and employment growth by job field, 1999 to 2009

Every profession saw salary increases from 1999 to 2009.  For reference, inflation over that same time period was 28%. So in reality, some of the jobs towards the right of the plot more or less broke even, while personal care and services actually lost money.  The raw number of managers has actually decreased over the last 10 years, however their salaries have increased faster than any other profession.  The negative employment percentages towards the right of the graph could be attributed to the recession and high unemployment rate in 2009.

Finally, the high level categories in the previous plots don't capture the whole picture.  There is quite a bit of variation in job types and salaries within each category.  Below is a detailed table highlighting the main jobs in each category.  I had to do some pruning and cleanup on the raw data out of the Bureau of Labor Statistics.  Only the main and/or easily recognizable jobs in each field are listed, so the totals for each field are more than the sum of the jobs listed below them.

	2009		1999		% Change
Title	# Employed	Average Salary	# Employed	Average Salary	# Employed	Average Salary
All Occupations	130,647,610	43,460
Management	6,116,380	102,900	8,063,410	64,740	-24%	59%
Chief executives	297,640	167,280	597,060	101,240	-50%	65%
General and operations managers	1,689,680	110,550	2,305,610	65,910	-27%	68%
Marketing managers	169,330	120,070	202,710	71,010	-16%	69%
Sales managers	328,980	111,570	367,640	69,560	-11%	60%
Financial managers	495,180	113,730	646,050	69,100	-23%	65%
Construction managers	204,760	93,290	240,490	60,160	-15%	55%
Engineering managers	178,110	122,810	248,210	81,560	-28%	51%
Business and Financial	6,063,670	65,900	4,361,980	46,100	39%	43%
Claims adjusters, examiners, and investigators	273,930	58,780	154,770	41,960	77%	40%
Business operations specialists	1,036,450	65,960
Accountants and auditors	1,106,980	67,430	843,160	44,320	31%	52%
Financial analysts	235,240	85,240	142,820	56,340	65%	51%
Personal financial advisors	149,460	94,180	79,970	64,680	87%	46%
Loan officers	298,200	63,210	200,180	45,210	49%	40%
Engineering	5,716,420	74,940	5,126,460	53,265	12%	41%
Computer software engineers	880,700	93,395	496,630	66,005	77%	41%
Network and computer systems administrators	338,890	70,930	204,680	50,090	66%	42%
Architects	101,630	78,880	71,040	53,410	43%	48%
Surveyors	50,360	57,420	50,150	36,400	0%	58%
Aerospace engineers	70,570	96,270	71,790	64,550	-2%	49%
Biomedical engineers	14,760	82,550	6,450	52,430	129%	57%
Chemical engineers	29,000	91,670	28,630	64,250	1%	43%
Civil engineers	259,320	81,180	209,100	55,660	24%	46%
Computer hardware engineers	65,410	101,410	60,420	66,960	8%	51%
Electrical engineers	151,660	86,250	149,210	61,520	2%	40%
Environmental engineers	50,610	80,750	51,450	57,050	-2%	42%
Industrial engineers	209,300	77,090	155,910	57,450	34%	34%
Mechanical engineers	232,660	80,580	202,910	57,010	15%	41%
Nuclear engineers	16,710	100,350	9,580	72,870	74%	38%
Petroleum engineers	25,540	119,960	9,640	72,780	165%	65%
Engineering technicians	514,060	49,496	566,000	38,593	-9%	28%
Science	1,308,380	65,660	909,530	45,660	44%	44%
Biochemists and biophysicists	22,860	88,550	11,810	56,170	94%	58%
Microbiologists	16,260	71,980	15,630	50,690	4%	42%
Zoologists and wildlife biologists	17,460	60,670	11,120	43,400	57%	40%
Biological scientists	29,630	69,430
Medical scientists	101,760	84,760	21,200	55,880	380%	52%
Life scientists	12,320	72,590
Astronomers	1,240	102,740	680	75,860	82%	35%
Physicists	13,630	111,250	10,290	76,140	32%	46%
Atmospheric and space scientists	8,320	85,160	7,170	53,580	16%	59%
Chemists	79,910	72,740	73,840	51,580	8%	41%
Environmental scientists	83,530	67,360	53,610	47,000	56%	43%
Geoscientists	31,860	92,710	20,940	61,000	52%	52%
Economists	13,160	96,320	14,490	61,550	-9%	56%
Market research analysts	226,410	67,500	67,670	52,680	235%	28%
Psychologists	108,590	78,265	92,460	49,720	17%	57%
Anthropologists and archeologists	5,570	57,230	3,220	37,010	73%	55%
Historians	3,620	56,350	1,510	41,350	140%	36%
Political scientists	3,970	101,050	4,280	72,860	-7%	39%
Social scientists	29,250	73,450
Biological technicians	74,560	41,140	39,580	32,060	88%	28%
Chemical technicians	64,420	43,900	78,730	36,080	-18%	22%
Social Services	1,891,320	42,750	1,404,540	31,640	35%	35%
Substance abuse and behavioral disorder counselors	78,470	40,420	57,290	28,560	37%	42%
Educational, vocational, and school counselors	251,050	55,030	190,930	41,490	31%	33%
Marriage and family therapists	26,450	49,020	18,530	35,660	43%	37%
Mental health counselors	106,920	41,710	62,910	29,430	70%	42%
Rehabilitation counselors	112,690	34,710	93,130	26,520	21%	31%
Child, family, and school social workers	277,670	43,540	262,570	31,720	6%	37%
Medical and public health social workers	133,510	48,340	101,680	35,400	31%	37%
Mental health and substance abuse social workers	127,140	41,350	72,730	31,150	75%	33%
Probation officers and correctional treatment specialists	92,910	50,500	78,930	38,030	18%	33%
Social and human service assistants	344,050	29,880	242,530	22,760	42%	31%
Clergy	42,670	46,960	26,000	32,210	64%	46%
Legal	999,020	95,820	858,320	66,780	16%	43%
Lawyers	556,790	129,020	464,250	90,360	20%	43%
Judges, magistrate judges, and magistrates	26,350	103,990	23,150	67,150	14%	55%
Paralegals and legal assistants	246,810	50,080	175,870	36,550	40%	37%
Education	8,488,740	49,530	7,344,830	36,040	16%	37%
Postsecondary teachers	1,392,850	73,387	798,010	52,421	75%	40%
Preschool teachers	389,660	27,450	339,310	19,610	15%	40%
Kindergarten teachers	181,810	50,380	158,250	36,770	15%	37%
Elementary school teachers	1,544,300	53,150	1,357,340	39,560	14%	34%
Middle school teachers	665,420	53,550	570,010	39,690	17%	35%
Secondary school teachers	1,091,710	55,150	947,010	41,430	15%	33%
Vocational education teachers	92,980	54,420	107,330	41,710	-13%	30%
Special education teachers	477,310	54,980	410,410	40,357	16%	36%
Adult literacy, remedial education, and GED teachers and instructors	68,430	50,390	56,880	32,800	20%	54%
Librarians	150,520	55,670	137,760	41,270	9%	35%
Teacher assistants	1,275,410	24,280	1,115,820	17,400	14%	40%
Arts, Entertainment, Sports, and Media	1,745,670	51,720	1,551,600	37,650	13%	37%
Art directors	31,660	91,520	19,190	61,680	65%	48%
Multi-media artists and animators	28,800	62,810	30,530	41,330	-6%	52%
Commercial and industrial designers	29,170	61,400	38,350	47,910	-24%	28%
Fashion designers	15,780	74,410	9,600	52,580	64%	42%
Floral designers	51,470	24,940	59,410	18,980	-13%	31%
Graphic designers	200,870	47,820	119,820	36,210	68%	32%
Interior designers	46,010	51,990	29,690	38,360	55%	36%
Merchandise displayers and window trimmers	61,280	28,480	51,530	21,560	19%	32%
Actors	39,880	*	84,790	50,620	-53%
Producers and directors	79,780	86,870	39,200	47,230	104%	84%
Athletes and sports competitors	13,620	80,950	10,620	69,440	28%	17%
Coaches and scouts	179,830	35,740	65,820	32,010	173%	12%
Umpires, referees, and other sports officials	14,860	28,490	8,150	23,510	82%	21%
Dancers	10,700	*	14,910	24,750	-28%
Choreographers	14,700	42,130	11,170	32,370	32%	30%
Music directors and composers	14,330	53,410	6,310	34,750	127%	54%
Musicians and singers	47,260	*	46,440	37,510	2%
Radio and television announcers	42,410	38,860	50,410	25,640	-16%	52%
Reporters, correspondents, analysts	51,950	55,630	64,590	35,270	-20%	58%
Public relations specialists	242,670	59,370	118,280	40,780	105%	46%
Editors	105,040	58,440	95,210	42,030	10%	39%
Technical writers	46,270	65,610	46,680	46,940	-1%	40%
Writers and authors	43,390	64,560	45,670	45,500	-5%	42%
Audio and video equipment technicians	46,070	42,450	39,090	34,020	18%	25%
Sound engineering technicians	15,560	53,940	9,380	35,090	66%	54%
Photographers	57,760	36,370	66,070	25,710	-13%	41%
Camera operators, television, video, and motion picture	17,540	49,590	17,330	31,730	1%	56%
Film and video editors	17,550	63,680	12,770	44,380	37%	43%
Healthcare Practitioners	7,200,950	69,690	6,001,950	45,250	20%	54%
Chiropractors	26,310	80,390	11,540	70,930	128%	13%
Dentists	86,270	156,850	69,360	106,130	24%	48%
Orthodontists	5,410	206,190
Dietitians and nutritionists	53,220	53,230	41,320	37,350	29%	43%
Optometrists	26,480	106,960	21,400	77,750	24%	38%
Pharmacists	267,860	106,630	226,300	63,030	18%	69%
Anesthesiologists	37,450	211,750	25,910	123,780	45%	71%
Family and general practitioners	99,000	168,550	134,490	104,090	-26%	62%
Internists, general	48,270	183,990	48,740	123,280	-1%	49%
Obstetricians and gynecologists	20,380	204,470	18,780	135,430	9%	51%
Pediatricians, general	29,460	161,410	18,940	112,760	56%	43%
Psychiatrists	22,210	163,660	17,870	103,660	24%	58%
Surgeons	44,560	219,770	48,450	135,660	-8%	62%
Physician assistants	76,900	84,830	56,750	50,650	36%	67%
Podiatrists	9,720	131,730	4,470	100,090	117%	32%
Registered nurses	2,583,770	66,530	2,205,430	44,470	17%	50%
Occupational therapists	97,840	70,680	78,950	51,910	24%	36%
Physical therapists	174,490	76,220	131,050	58,350	33%	31%
Veterinarians	54,130	90,110	39,250	66,060	38%	36%
Medical and clinical laboratory technologists	166,860	55,620	145,750	39,310	14%	41%
Dental hygienists	173,900	67,860	90,050	48,150	93%	41%
Cardiovascular technologists and technicians	48,070	49,730	41,490	33,280	16%	49%
Diagnostic medical sonographers	51,630	63,640	29,280	43,760	76%	45%
Nuclear medicine technologists	21,670	68,450	17,880	42,430	21%	61%
Emergency medical technicians and paramedics	217,920	33,020	172,360	23,280	26%	42%
Dietetic technicians	24,510	28,530	29,190	21,000	-16%	36%
Pharmacy technicians	331,890	28,940	196,430	20,050	69%	44%
Veterinary technologists and technicians	79,200	30,580	47,470	21,430	67%	43%
Opticians, dispensing	60,840	34,790	58,860	25,190	3%	38%
Athletic trainers	15,260	44,020	16,670	33,650	-8%	31%
Healthcare Support	3,886,690	26,710	2,970,780	19,780	31%	35%
Home health aides	955,220	21,620	577,530	18,810	65%	15%
Nursing aides, orderlies, and attendants	1,438,010	24,980	1,308,740	17,860	10%	40%
Psychiatric aides	62,610	27,430	51,100	22,390	23%	23%
Massage therapists	55,920	39,780	21,910	28,740	155%	38%
Dental assistants	294,020	34,000	175,160	24,130	68%	41%
Medical assistants	495,970	29,450	281,480	22,650	76%	30%
Protective Services	3,172,420	41,740	2,958,730	29,650	7%	41%
Fire fighters	305,500	47,270	252,730	34,070	21%	39%
Correctional officers and jailers	455,350	42,610	381,250	31,070	19%	37%
Detectives and criminal investigators	110,380	65,860	83,340	47,620	32%	38%
Fish and game wardens	7,530	54,950	8,220	41,940	-8%	31%
Police and sheriff's patrol officers	641,590	55,180	581,860	38,710	10%	43%
Animal control workers	15,320	33,560	8,300	23,850	85%	41%
Private detectives and investigators	31,250	47,130	30,690	30,120	2%	56%
Security guards	1,028,830	26,430	1,088,470	18,610	-5%	42%
Crossing guards	68,470	25,430	68,310	17,870	0%	42%
Lifeguards, ski patrol, and other recreational protective service workers	115,640	20,490
Food Preparation and Serving	11,218,260	20,880	9,687,970	15,600	16%	34%
Chefs and head cooks	94,300	44,240	118,070	28,040	-20%	58%
Cooks, fast food	539,520	18,230	418,400	13,610	29%	34%
Cooks, institution and cafeteria	383,540	23,870	438,660	17,420	-13%	37%
Cooks, restaurant	898,820	23,110	656,540	17,730	37%	30%
Food preparation workers	849,400	20,420	878,650	15,740	-3%	30%
Bartenders	492,480	20,970	358,450	14,700	37%	43%
Waiters and waitresses	2,302,070	20,380	2,039,950	13,430	13%	52%
Dishwashers	512,990	18,330	538,360	14,090	-5%	30%
Cleaning and Maintenance	4,269,480	24,970	4,274,200	18,910	0%	32%
Janitors	2,090,400	24,120	2,090,560	18,220	0%	32%
Maids and housekeeping cleaners	887,890	20,840	913,470	15,530	-3%	34%
Pest control workers	63,500	32,100	40,240	24,120	58%	33%
Landscaping and groundskeeping workers	859,960	25,340	739,460	19,380	16%	31%
Tree trimmers and pruners	37,830	32,090	47,890	23,770	-21%	35%
Personal Care and Service	3,461,910	24,680	2,556,920	20,300	35%	22%
Gaming dealers	86,900	20,290	87,390	14,120	-1%	44%
Ushers, lobby attendants, and ticket takers	104,360	19,610	88,590	14,050	18%	40%
Amusement and recreation attendants	257,350	19,450	190,600	14,920	35%	30%
Barbers	10,550	27,650	14,150	20,970	-25%	32%
Hairdressers, hairstylists, and cosmetologists	349,210	27,070	314,750	20,800	11%	30%
Baggage porters and bellhops	49,380	23,580	59,580	17,110	-17%	38%
Concierges	20,470	28,760	16,440	22,420	25%	28%
Tour guides and escorts	31,630	25,990	35,780	20,100	-12%	29%
Flight attendants	95,810	43,350	123,310	47,910	-22%	-10%
Child care workers	595,650	20,940	377,110	15,430	58%	36%
Personal and home care aides	630,740	20,280	300,500	16,060	110%	26%
Fitness trainers and aerobics instructors	228,170	35,340	127,310	27,300	79%	29%
Sales	13,715,050	36,020	12,938,130	27,060	6%	33%
Cashiers	3,439,380	19,030	3,162,090	15,290	9%	24%
Counter and rental clerks	416,950	24,680	392,560	16,690	6%	48%
Parts salespersons	208,350	30,460	265,380	25,410	-21%	20%
Retail salespersons	4,209,500	24,630	3,729,040	19,210	13%	28%
Advertising sales agents	152,420	53,190	142,830	41,400	7%	28%
Insurance sales agents	325,710	61,330	241,730	47,690	35%	29%
Travel agents	76,990	32,450	111,130	24,660	-31%	32%
Demonstrators and product promoters	80,910	26,640	95,160	21,420	-15%	24%
Models	1,510	36,420	5,220	21,110	-71%	73%
Real estate brokers	48,380	78,360	26,760	62,190	81%	26%
Real estate sales agents	151,550	53,100	107,680	36,990	41%	44%
Telemarketers	307,730	24,760	485,650	21,100	-37%	17%
Door-to-door sales workers	8,460	26,320	36,130	28,940	-77%	-9%
Office and Administrative Support	22,336,450	32,990	22,562,480	25,310	-1%	30%
Bill and account collectors	403,100	32,560	383,090	24,860	5%	31%
Billing and posting clerks and machine operators	493,780	32,900	551,410	23,880	-10%	38%
Bookkeeping, accounting, and auditing clerks	1,757,870	34,750	1,619,870	25,250	9%	38%
Tellers	576,580	24,780	453,140	18,330	27%	35%
Customer service representatives	2,195,860	32,410	1,789,620	25,360	23%	28%
Receptionists and information clerks	1,052,120	26,010	987,680	19,870	7%	31%
Postal service mail carriers	339,030	48,940	352,550	36,610	-4%	34%
Shipping, receiving, and traffic clerks	715,130	29,840	886,230	22,080	-19%	35%
Stock clerks and order fillers	1,864,410	23,460	1,800,840	19,650	4%	19%
Executive secretaries and administrative assistants	1,361,170	44,010	1,316,290	30,870	3%	43%
Secretaries	1,797,670	31,060	1,582,080	24,130	14%	29%
Farming	419,200	23,990	463,360	18,000	-10%	33%
Agricultural inspectors	14,030	41,860	10,520	30,080	33%	39%
Graders and sorters, agricultural products	40,160	20,640	62,380	15,520	-36%	33%
Agricultural equipment operators	22,420	25,220	17,630	17,640	27%	43%
Farmworkers and laborers	233,650	19,780	215,080	14,150	9%	40%
Fishers and related fishing workers	670	26,600
Forest and conservation workers	5,840	29,410	11,780	20,120	-50%	46%
Logging equipment operators	23,630	32,870	33,230	25,310	-29%	30%
Log graders and scalers	2,940	35,550	5,500	26,180	-47%	36%
Construction and Extraction	5,751,630	43,350	5,938,860	33,650	-3%	29%
Brickmasons and blockmasons	87,780	49,250	98,530	41,380	-11%	19%
Carpenters	743,760	43,640	771,030	34,420	-4%	27%
Cement masons and concrete finishers	165,700	39,410	151,760	31,210	9%	26%
Construction laborers	856,440	33,190	763,450	26,510	12%	25%
Construction equipment operators	368,200	44,180	324,350	34,760	14%	27%
Drywall and ceiling tile installers	102,880	41,080	118,300	34,090	-13%	21%
Electricians	579,150	50,850	611,920	42,180	-5%	21%
Painters, construction and maintenance	214,240	37,320	260,880	29,280	-18%	27%
Plumbers, pipefitters, and steamfitters	400,970	49,870	413,170	38,750	-3%	29%
Roofers	108,180	37,390	115,280	29,870	-6%	25%
Sheet metal workers	146,690	44,890	231,690	33,110	-37%	36%
Construction and building inspectors	90,730	53,550	67,010	39,740	35%	35%
Highway maintenance workers	139,490	35,310	139,540	26,730	0%	32%
Roustabouts, oil and gas	61,320	34,190	29,860	23,260	105%	47%
Installation, Maintenance, and Repair	5,114,150	42,210	5,140,210	32,810	-1%	29%
Telecommunications equipment installers	189,850	52,990	172,700	41,130	10%	29%
Security and fire alarm systems installers	63,690	39,830	38,350	30,810	66%	29%
Aircraft mechanics and service technicians	112,130	52,970	125,970	39,280	-11%	35%
Automotive service technicians and mechanics	606,990	37,880	587,320	30,130	3%	26%
Bus and truck mechanics and diesel engine specialists	232,810	41,590	273,320	31,800	-15%	31%
Heating and air conditioning mechanics	244,410	43,670	187,850	32,040	30%	36%
Industrial machinery mechanics	276,230	46,160	176,070	36,210	57%	27%
Maintenance and repair workers, general	1,268,930	36,520	1,201,690	26,930	6%	36%
Telecommunications line installers and repairers	162,400	48,310	158,990	35,790	2%	35%
Production	8,927,130	33,290	12,620,920	25,400	-29%	31%
Electrical and electronic equipment assemblers	193,570	30,690	387,430	21,840	-50%	41%
Team assemblers	997,390	28,840	1,302,820	22,200	-23%	30%
Assemblers and fabricators, all other	267,780	32,280
Bakers	140,510	25,350	176,080	19,990	-20%	27%
Butchers and meat cutters	125,510	30,270	138,870	24,890	-10%	22%
Meat, poultry, and fish cutters and trimmers	168,700	22,900	159,890	17,370	6%	32%
Cutting, punching, and press machine setters, operators, and tenders, metal and plastic	209,730	30,480	353,300	23,640	-41%	29%
Machinists	380,720	38,940	419,800	30,540	-9%	28%
Welders, cutters, solderers, and brazers	357,740	36,630	410,040	27,870	-13%	31%
Laundry and dry-cleaning workers	211,490	20,790	217,350	15,760	-3%	32%
Power plant operators	36,860	60,270	34,310	43,110	7%	40%
Chemical plant and system operators	45,750	54,010	64,320	39,330	-29%	37%
Gas plant operators	14,040	55,860	16,740	43,080	-16%	30%
Inspectors, testers, sorters, samplers, and weighers	430,450	34,840	577,650	27,140	-25%	28%
Jewelers and precious stone and metal workers	23,410	36,620	28,690	26,360	-18%	39%
Packaging and filling machine operators and tenders	338,920	27,320	379,760	20,790	-11%	31%
Transportation	8,844,700	32,180	9,538,820	24,630	-7%	31%
Airline pilots, copilots, and flight engineers	74,420	117,060	88,040	98,280	-15%	19%
Commercial pilots	29,180	73,060	18,780	56,240	55%	30%
Air traffic controllers	24,420	106,990	22,620	73,190	8%	46%
Bus drivers, transit and intercity	177,510	35,990	160,210	26,450	11%	36%
Bus drivers, school	459,480	28,050	463,860	20,460	-1%	37%
Driver/sales workers	363,050	26,690	385,210	22,520	-6%	19%
Truck drivers, heavy and tractor-trailer	1,550,930	39,260	1,558,400	31,900	0%	23%
Truck drivers, light or delivery services	834,780	31,120	1,085,050	23,530	-23%	32%
Taxi drivers and chauffeurs	167,740	23,930	119,630	18,200	40%	31%
Locomotive engineers	43,560	53,590	19,940	48,050	118%	12%
Subway and streetcar operators	6,050	52,800
Sailors and marine oilers	31,950	37,310	27,200	25,820	17%	45%
Captains, mates, and pilots of water vessels	30,450	70,740	20,660	41,460	47%	71%
Parking lot attendants	129,990	20,600	109,340	15,350	19%	34%
Service station attendants	79,480	20,820	109,050	15,770	-27%	32%
Crane and tower operators	40,770	47,700	53,830	33,710	-24%	42%
Excavating and loading machine and dragline operators	57,990	38,540	62,360	31,460	-7%	23%
Industrial truck and tractor operators	568,270	31,240	590,710	25,650	-4%	22%
Cleaners of vehicles and equipment	298,500	22,110	302,380	16,650	-1%	33%
Freight, stock, and material movers	2,135,790	25,290	2,035,640	19,750	5%	28%
Packers and packagers, hand	706,240	21,780	1,114,330	16,280	-37%	34%
Refuse and recyclable material collectors	128,940	33,760	135,320	25,020	-5%	35%

References:

http://www.bls.gov