Media Studies Chapter 5 Homework The number of channels can be set in the input channel dropdown

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Lab: Digital Audio Manipulation

SoftwareRequirement:Audacity1.2orabove.Theinstructionsandscreenshotsusedherewerebased

fromAudacity1.3Beta.

Objectives of this lab:

1. Distinguishbetweenaudiosamplingrateandaudiofrequency

2. RecordavoiceinAudacity,removebackgroundnoise,rearrangethewaveform,andapply

soundeffects

3. Frequencyanalysisofhumanvoice

5. LearnwhattypeofinformationislostwhensavingMP3files

Lab Instructions:

I.DistinguishAudioSamplingRatefromAudioFrequency

Downloadfoursingletonesfilesfromthebook’sWebsite.Listentothesefoursingletones.Notethe

differenceinthepitch.

Thesamplingratesandtheaudiofrequenciesofthesesingletonesarelistedinthefollowingtable:



FileFilenameSamplingRateBaseFrequencyoftheSingle‐tone



Q1.Multiple‐choice:Withthesamebasefrequencyofthetone,increasingtheaudio

A.increasesthepitchofthetone

B.decreasesthepitchofthetone

C.doesnotchangethepitchofthetone



Q2.Multiple‐choice:Withthesamesamplingrate,increasingthebasefrequencyof

A.increasesthepitchofthetone

B.decreasesthepitchofthetone

C.doesnotchangethepitchofthetone



III.Recordyourvoiceandremovethebackgroundnoise

1) CreateanewfileinAudacity.Todoso:

SelectFile>New.Setthesettingsasfollows:

Qualityontheleftpane(Figure1).Thenumberofchannelscanbesetintheinputchannel



2) Recordyourvoice,saying“abc”.Tostartrecording,clicktherecordbutton(Figure3).



3) Applyanoisereductionasshowninthetutorialtoremovethebackgroundnoise.

Todothis:

i. Selectaportionofthewaveformthathasjust“noise”(forexample,thesegmentatthe



IV. Rearrange the waveform

1) Withthevoice.wavstillopeninAudacity,rearrangeyouraudioabovetosound“cab”by

V. Frequency analysis of human voice



2) SettheFFTSizeto1024andothersettingsasshowninFigure5.



Q3.Multiple‐choice:Inthefrequencyanalysisgraph,youmaynoticethatthehigh

amplitudeconcentratesonacertainrangeoffrequency,whichistherangeof

audiofrequencyofyourspeechinthisrecording.



Fromthefrequencyanalysisofyourspeechandotherstudents’(lookatother

students’ifpossible),whatistherangeofaudiofrequencyofhumanspeech?A

waveforminAuditionalsoappliesinAudacity.

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Figure5.Frequencyanalysiswindow

VI. Audio file type: .WAV vs. .MP3; and MP3 being lossy compression

1) Openmusic.wavinAudacity.Dothefollowingstepstosavethefileasmusic.mp3:

i. File>Export…



Q4.Multiple‐choice:Whichfile’ssizeissmaller?B



2) Closemusic.mp3andreopenitinAudacity.

(Youneedtoclosethefileandreopenitinordertoseetheeffectinthenextstep.)



3) Lookatthespectralviewofbothmusic.wavandmusic.mp3.

Note:Tolookatthespectralviewofanaudiofile,selectSpectrumfromtheAudioTrack

dropdown(Figure6)ofthetrackthattheaudioisin.

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Figure6.TheSpectrumoptioncanbefoundintheAudioTrackdropdownontheleftofeachtrack.



Thespectralview(Figure7)showstheaudiofrequencyversustime.Theintensityofthecolor



Q5.Multiple‐choice:Bycomparingthespectralviewofmusic.wavandmusic.mp3,

youseesomeaudiofrequencyrangesarelostinthemusic.mp3file.Which

A.thehighfrequencyrange

B.thelowfrequencyrange



ThefrequencyrangethatislostintheMP3fileisnotperceivablebytheaveragehumanearinthe

presenceoftheotheraudiofrequencyrangesinthefile.ThisisthebasicideaoftheMP3compression.

That’swhythefilesizeofMP3canbesosmall;ithasmuchlessdataandthedataisnotexactlythe

sameastheoriginaluncompressedfile.Butitstillsoundsgood.



4) TohearwhatislostinthisMP3file,downloadthefilemusic-lost-in-mp3.wav,andplayit.

Thisfilewascreatedbycopyingtheregionabove16,000Hzfromthespectralviewofthe

music.wavinAdobeAuditionandpastingitintoanewfile.



Dependingonyourcomputer’ssoundcardandyourcomputerspeaker,youmayormaynotbe

abletohearthishighfrequencyrange.



X. Apply a pitch-change audio effect to your audio



2) Changethepitchoftheaudio(Effect>ChangePitch)bymovingtheslidersorselectingapreset

ofyourchoicefromthePresetsdropdown.



3) ClickOK,andplaytothestretchedandpitchshiftedaudio.Savethefile.

XI. Apply an echo effect to your audio



2) Applyanechoeffect(Effect>Echo…).



Tips:Thebasicideaofcreatingechoesisrepeatingtheaudiowithsomedelay,witheach

repetitionslightlysofterthanthepreviousone.Thedelaytimesettinginthedialogboxdefines

howmuchtimebetweeneachrepetitionoftheaudio,andthedecayfactorspecifichowmuch

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3) Savethefile.

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