{"group":{"id":1,"name":"Community","lockable":false,"created_at":"2012-01-18T18:02:15.000Z","updated_at":"2026-05-26T00:16:20.000Z","description":"Problems submitted by members of the MATLAB Central community.","is_default":true,"created_by":161519,"badge_id":null,"featured":false,"trending":false,"solution_count_in_trending_period":0,"trending_last_calculated":"2026-05-26T00:00:00.000Z","image_id":null,"published":true,"community_created":false,"status_id":2,"is_default_group_for_player":false,"deleted_by":null,"deleted_at":null,"restored_by":null,"restored_at":null,"description_opc":null,"description_html":null,"published_at":null},"problems":[{"id":60834,"title":"Bell 202 Decoder","description":"Decode an audio frequency shift key stream at a certain baud-rate and sample rate into a binary stream of data using the Bell 202 standard. \r\nWhere a '1' is represented as 1200 Hz and a  '0' is represnted as 2200 Hz.\r\nDuration of each bit is based on the baud-rate.\r\nDigitized audio stream is produced at the sample rate and is smooth between bits.","description_html":"\u003cdiv style = \"text-align: start; line-height: 20.44px; min-height: 0px; white-space: normal; color: rgb(0, 0, 0); font-family: Menlo, Monaco, Consolas, monospace; font-style: normal; font-size: 14px; font-weight: 400; text-decoration: none solid rgb(0, 0, 0); white-space: normal; \"\u003e\u003cdiv style=\"block-size: 132px; display: block; min-width: 0px; padding-block-start: 0px; padding-top: 0px; perspective-origin: 408px 66px; transform-origin: 408px 66px; vertical-align: baseline; \"\u003e\u003cdiv style=\"block-size: 42px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 385px 21px; text-align: left; transform-origin: 385px 21px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 0px 0px; transform-origin: 0px 0px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eDecode an audio frequency shift key stream at a certain baud-rate and sample rate into a binary stream of data using the Bell 202 standard. \u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003cdiv style=\"block-size: 21px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 385px 10.5px; text-align: left; transform-origin: 385px 10.5px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 0px 0px; transform-origin: 0px 0px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eWhere a '1' is represented as 1200 Hz and a  '0' is represnted as 2200 Hz.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003cdiv style=\"block-size: 21px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 385px 10.5px; text-align: left; transform-origin: 385px 10.5px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 0px 0px; transform-origin: 0px 0px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eDuration of each bit is based on the baud-rate.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003cdiv style=\"block-size: 21px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 385px 10.5px; text-align: left; transform-origin: 385px 10.5px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 0px 0px; transform-origin: 0px 0px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eDigitized audio stream is produced at the sample rate and is smooth between bits.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e","function_template":"function decodedStream = decodeBell202(audioSignal, sampleRate, bitRate)\r\n decodedStream=audioSignal/bitRate;\r\nend","test_suite":"%%\r\nrng(2718);\r\nbS=num2str(randi(2,1,1e4)-1);\r\nbS(bS==' ')=[];\r\nt = 1/1e5:1/1e5:1/9.2e2;\r\naS=[];\r\np=0;\r\nfor i = 1:length(bS)\r\n   if isequal(bS(i),'0')\r\n     aS=[aS, sin(2*pi*2200*t+p)];\r\n     p=atan2(aS(end),cos(2*pi*2200*t(end)+p));\r\n   else\r\n     aS=[aS, sin(2*pi*1200*t+p)];\r\n     p=atan2(aS(end),cos(2*pi*1200*t(end)+p));\r\n   end\r\nend\r\nassert(isequal(decodeBell202(aS,1e5,920),bS))\r\n%%\r\nrng(2718);\r\nbS=num2str(randi(2,1,1e4)-1);\r\nbS(bS==' ')=[];\r\nt = 1/1e5:1/1e5:1/1e3;\r\naS=[];\r\np=0;\r\nfor i = 1:length(bS)\r\n   if isequal(bS(i),'0')\r\n     aS=[aS, sin(2*pi*2200*t+p)];\r\n     p=atan2(aS(end),cos(2*pi*2200*t(end)+p));\r\n   else\r\n     aS=[aS, sin(2*pi*1200*t+p)];\r\n     p=atan2(aS(end),cos(2*pi*1200*t(end)+p));\r\n   end\r\nend\r\nassert(isequal(decodeBell202(aS,1e5,1e3),bS))\r\n%%\r\nbS='1011110001100110011001110001110101011010101010111000111000111000111100011100110101011001';\r\nt = 1/1.2e5:1/1.2e5:1/600;\r\naS=[];\r\np=0;\r\nfor i = 1:length(bS)\r\n   if isequal(bS(i),'0')\r\n     aS=[aS, sin(2*pi*2200*t+p)];\r\n     p=atan2(aS(end),cos(2*pi*2200*t(end)+p));\r\n   else\r\n     aS=[aS, sin(2*pi*1200*t+p)];\r\n     p=atan2(aS(end),cos(2*pi*1200*t(end)+p));\r\n   end\r\nend\r\nassert(isequal(decodeBell202(aS,1.2e5,600),bS))\r\n%%","published":true,"deleted":false,"likes_count":0,"comments_count":0,"created_by":145982,"edited_by":null,"edited_at":null,"deleted_by":null,"deleted_at":null,"solvers_count":5,"test_suite_updated_at":null,"rescore_all_solutions":false,"group_id":1,"created_at":"2025-03-27T15:12:44.000Z","updated_at":"2025-12-07T15:19:32.000Z","published_at":"2025-03-27T15:12:43.000Z","restored_at":null,"restored_by":null,"spam":null,"simulink":false,"admin_reviewed":false,"description_opc":"{\"parts\":[{\"partUri\":\"/matlab/document.xml\",\"contentType\":\"application/vnd.mathworks.matlab.code.document+xml\",\"content\":\"\u003c?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\"?\u003e\u003cw:document xmlns:w=\\\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\\\"\u003e\u003cw:body\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eDecode an audio frequency shift key stream at a certain baud-rate and sample rate into a binary stream of data using the Bell 202 standard. \u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eWhere a '1' is represented as 1200 Hz and a  '0' is represnted as 2200 Hz.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eDuration of each bit is based on the baud-rate.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eDigitized audio stream is produced at the sample rate and is smooth between bits.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003c/w:body\u003e\u003c/w:document\u003e\",\"relationship\":null}],\"relationships\":[{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/document\",\"target\":\"/matlab/document.xml\",\"relationshipId\":\"rId1\"}]}"}],"problem_search":{"problems":[{"id":60834,"title":"Bell 202 Decoder","description":"Decode an audio frequency shift key stream at a certain baud-rate and sample rate into a binary stream of data using the Bell 202 standard. \r\nWhere a '1' is represented as 1200 Hz and a  '0' is represnted as 2200 Hz.\r\nDuration of each bit is based on the baud-rate.\r\nDigitized audio stream is produced at the sample rate and is smooth between bits.","description_html":"\u003cdiv style = \"text-align: start; line-height: 20.44px; min-height: 0px; white-space: normal; color: rgb(0, 0, 0); font-family: Menlo, Monaco, Consolas, monospace; font-style: normal; font-size: 14px; font-weight: 400; text-decoration: none solid rgb(0, 0, 0); white-space: normal; \"\u003e\u003cdiv style=\"block-size: 132px; display: block; min-width: 0px; padding-block-start: 0px; padding-top: 0px; perspective-origin: 408px 66px; transform-origin: 408px 66px; vertical-align: baseline; \"\u003e\u003cdiv style=\"block-size: 42px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 385px 21px; text-align: left; transform-origin: 385px 21px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 0px 0px; transform-origin: 0px 0px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eDecode an audio frequency shift key stream at a certain baud-rate and sample rate into a binary stream of data using the Bell 202 standard. \u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003cdiv style=\"block-size: 21px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 385px 10.5px; text-align: left; transform-origin: 385px 10.5px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 0px 0px; transform-origin: 0px 0px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eWhere a '1' is represented as 1200 Hz and a  '0' is represnted as 2200 Hz.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003cdiv style=\"block-size: 21px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 385px 10.5px; text-align: left; transform-origin: 385px 10.5px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 0px 0px; transform-origin: 0px 0px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eDuration of each bit is based on the baud-rate.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003cdiv style=\"block-size: 21px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 385px 10.5px; text-align: left; transform-origin: 385px 10.5px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 0px 0px; transform-origin: 0px 0px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eDigitized audio stream is produced at the sample rate and is smooth between bits.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e","function_template":"function decodedStream = decodeBell202(audioSignal, sampleRate, bitRate)\r\n decodedStream=audioSignal/bitRate;\r\nend","test_suite":"%%\r\nrng(2718);\r\nbS=num2str(randi(2,1,1e4)-1);\r\nbS(bS==' ')=[];\r\nt = 1/1e5:1/1e5:1/9.2e2;\r\naS=[];\r\np=0;\r\nfor i = 1:length(bS)\r\n   if isequal(bS(i),'0')\r\n     aS=[aS, sin(2*pi*2200*t+p)];\r\n     p=atan2(aS(end),cos(2*pi*2200*t(end)+p));\r\n   else\r\n     aS=[aS, sin(2*pi*1200*t+p)];\r\n     p=atan2(aS(end),cos(2*pi*1200*t(end)+p));\r\n   end\r\nend\r\nassert(isequal(decodeBell202(aS,1e5,920),bS))\r\n%%\r\nrng(2718);\r\nbS=num2str(randi(2,1,1e4)-1);\r\nbS(bS==' ')=[];\r\nt = 1/1e5:1/1e5:1/1e3;\r\naS=[];\r\np=0;\r\nfor i = 1:length(bS)\r\n   if isequal(bS(i),'0')\r\n     aS=[aS, sin(2*pi*2200*t+p)];\r\n     p=atan2(aS(end),cos(2*pi*2200*t(end)+p));\r\n   else\r\n     aS=[aS, sin(2*pi*1200*t+p)];\r\n     p=atan2(aS(end),cos(2*pi*1200*t(end)+p));\r\n   end\r\nend\r\nassert(isequal(decodeBell202(aS,1e5,1e3),bS))\r\n%%\r\nbS='1011110001100110011001110001110101011010101010111000111000111000111100011100110101011001';\r\nt = 1/1.2e5:1/1.2e5:1/600;\r\naS=[];\r\np=0;\r\nfor i = 1:length(bS)\r\n   if isequal(bS(i),'0')\r\n     aS=[aS, sin(2*pi*2200*t+p)];\r\n     p=atan2(aS(end),cos(2*pi*2200*t(end)+p));\r\n   else\r\n     aS=[aS, sin(2*pi*1200*t+p)];\r\n     p=atan2(aS(end),cos(2*pi*1200*t(end)+p));\r\n   end\r\nend\r\nassert(isequal(decodeBell202(aS,1.2e5,600),bS))\r\n%%","published":true,"deleted":false,"likes_count":0,"comments_count":0,"created_by":145982,"edited_by":null,"edited_at":null,"deleted_by":null,"deleted_at":null,"solvers_count":5,"test_suite_updated_at":null,"rescore_all_solutions":false,"group_id":1,"created_at":"2025-03-27T15:12:44.000Z","updated_at":"2025-12-07T15:19:32.000Z","published_at":"2025-03-27T15:12:43.000Z","restored_at":null,"restored_by":null,"spam":null,"simulink":false,"admin_reviewed":false,"description_opc":"{\"parts\":[{\"partUri\":\"/matlab/document.xml\",\"contentType\":\"application/vnd.mathworks.matlab.code.document+xml\",\"content\":\"\u003c?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\"?\u003e\u003cw:document xmlns:w=\\\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\\\"\u003e\u003cw:body\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eDecode an audio frequency shift key stream at a certain baud-rate and sample rate into a binary stream of data using the Bell 202 standard. \u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eWhere a '1' is represented as 1200 Hz and a  '0' is represnted as 2200 Hz.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eDuration of each bit is based on the baud-rate.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eDigitized audio stream is produced at the sample rate and is smooth between bits.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003c/w:body\u003e\u003c/w:document\u003e\",\"relationship\":null}],\"relationships\":[{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/document\",\"target\":\"/matlab/document.xml\",\"relationshipId\":\"rId1\"}]}"}],"errors":[],"facets":[[],[{"value":"hard","count":1,"selected":false}]],"term":"tag:\"bell202\"","page":1,"per_page":50,"sort":"map(difficulty_value,0,0,999) asc"}}