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BSc!(Hons)!Music!Technology!
DIG6045!Technology!Project!UG3!
Assessment!1.2!–!Full!Project!Proposal!
October!2015!
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Developing*Real-Time*Reverb*for*Use*in*
Embedded*Systems*
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Harry!Lewis!
Supervisor:!Ryan!Stables!
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Table!of!Contents!
1.0!
Introduction!...............................................................................................!3!
1.1!Background!...........................................................................................................!3!
1.1.1!What!is!Reverb?!.............................................................................................!3!
1.1.2!Artificial!Reverb!..............................................................................................!4!
1.2!Scope!....................................................................................................................!5!
2.1!! Aim!...........................................................................................................!5!
2.2!! Objectives!.................................................................................................!5!
3.0!
Rationale!..................................................................................................!6!
4.0!
Tasks!and!Activities!..................................................................................!6!
4.1!Researching!different!reverb!design!methods!......................................................!6!
4.2!Comparing!the!Quality!of!Reverbs!........................................................................!6!
4.3!Developing!and!Testing!a!Reverb!........................................................................!7!
5.0!
Resources!................................................................................................!7!
6.0!
Literature!Search!Methodology!................................................................!7!
7.0!
Schedule!...................................................................................................!9!
8.0!
Risk!Assessment!......................................................................................!9!
9.0!
Ethics!Review!.........................................................................................!10!
10.0!
References!..........................................................................................!10!
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2!
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1.0! Introduction!
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1.1!Background!
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1.1.1!What!is!Reverb?!
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“Reverb'is'the'collective'name'given'to'the'sound'created'by'bounced'
reflections'from'room'boundaries”!(Izhaki,!2013).!!
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When!sound!is!created!in!an!enclosed!space,!the!sound!propagates!away!from!the!
source.!If!there!is!a!microphone!in!the!direct!path!of!the!sound!wave,!then!the!sound!
will!be!picked!up!by!the!microphone.!The!rest!of!the!sound!wave!however!will!keep!
travelling!and!will!eventually!hit!different!surfaces!and!some!of!the!sound!will!be!
reflected.!Some!of!these!reflections!will!travel!to!the!microphone!and!will!be!picked!up!
as!a!slightly!delayed,!and!quieter!versions!of!the!direct!sound!which!is!known!as!
reverb.!Humans!do!not!perceive!these!reflections!individually,!but!instead!they!are!
grouped!together!with!the!natural!sound!and!perceived!as!a!sense!of!acoustic!space!
(Mike!Senior,!2000).!
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Fig.'1';'Example'of'a'Generic'Room'Response'(Valimaki'et'al.,'2012)'
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3!
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Sound!will!arrive!at!the!listener!or!microphone!in!different!stages.!These!are!referred!to!
the!direct!sound,!the!early!reflections,!and!the!late!reverberation!(Fig.!1).!The!direct!
sound!goes!straight!from!the!source!to!the!microphone!as!stated!previously.!This!is!
followed!by!early!reflections!caused!from!nearby!objects!and!surfaces!(for!example!
bouncing!off!the!floor!between!source!and!listener).!Finally,!the!late!reverberation!is!
formed!of!a!dense!set!of!reflections!which!is!indicative!of!the!size!and!the!absorbing!
power!of!the!material!in!the!space!(Valimaki!et!al.,!2012).!These!different!stages!of!
reverberation!collectively!are!referred!to!the!impulse!response!which!essentially!
represents!the!character!of!the!space.!!
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1.1.2!Artificial!Reverb!
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Recordings!without!reverb!can!sometimes!be!described!as!sounding!very!“upbclose”,!
“dry”!or!“lifeless”,!so!in!situations!where!there!is!no!natural!reverb!in!the!room,!artificial!
reverb!can!be!added!to!enhance!the!recording.!Artificial!reverb!methods!are!made!up!
of:!acoustic!reverb!chambers,!plate!reverbs,!spring!reverbs!(all!of!which!are!analogue!
methods),!and!digital!reverb!(Hurtig,!1988).!The!latter!of!which!shall!be!the!focus!of!this!
project.!
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Older!hardware!digital!reverb!units!suffered!issues!with!sounding!like!a!real!space,!as!
the!algorithms!used!to!create!the!reverb!effect!were!not!based!on!the!principles!of!
natural!acoustics,!and!not!taking!into!account!things!like!frequency!and!early!
reflections.!Another!issue!was!a!lack!of!physical!memory!in!the!unit!itself!which!limited!
the!number!of!algorithms!that!could!be!stored!on!the!device!(Farquharson,!2007).!
Since!then,!computer!memory!and!processing!has!increased!hugely,!and!now!most!
well!specified!computers!can!run!computationally!taxing!artificial!reverb!processes!like!
convolution!reverb.!Simply!put,!this!is!where!the!impulse!response!of!a!space!is!
recorded!and!then!multiplied!by!every!sample!of!an!audio!signal!which!adds!the!rooms!
reverb!to!the!original!signal!(White,!2006).!
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1.2!Scope!
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This!project!will!investigate!and!compare!different!methods!of!creating!digital!reverb!
with!the!aim!of!being!able!to!implement!it!on!an!embedded!system!such!as!an!audio!
interface.!Any!testing!and!analysis!will!be!carried!out!purely!with!the!suitability!of!the!
reverb!being!applied!to!such!an!embedded!system!in!mind,!rather!than!its!suitability!in!
general.!!
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2.1!! Aim!
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This!project!aims!to!identify!and!develop!a!method!of!creating!a!realistic!sounding!and!
computationally!efficient!reverb!which!would!be!suitable!for!use!in!an!embedded!
system!with!limited!resources.!!
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2.2!! Objectives!
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•! To!identify!and!compare!different!methods!of!creating!reverb!and!their!
suitability!for!real!time!implementation.!
•! To!explore!the!realbtime!implications!of!combining!convolution!and!algorithmic!
reverb.!
•! To!devise!a!series!of!tests!to!quantify!the!quality!or!realism!of!a!reverb!using!
existing!methods.!
•! To!outline!a!minimum!reverb!quality!and!the!maximum!resources!available!to!
the!reverb!algorithm!in!an!embedded!system.!
•! To!devise!and!apply!a!series!of!tests!in!Matlab!to!benchmark!the!performance!
different!reverb!algorithms.!
•! To!develop!the!best!reverb!method!to!maximise!quality!and!efficiency!up!to!a!
point!that!meets!with!a!given!specification.!
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3.0! Rationale!
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The!ability!to!create!efficient!and!realistic!reverb!in!real!time!is!useful!for!commercial!
gain!as!well!as!furthering!the!field!of!reverb!in!academic!research.!Being!able!to!
include!a!high!quality!reverb!at!low!computational!cost,!without!the!need!for!extra!
processing!power!or!dedicated!hardware!chips,!is!beneficial!for!commercial!companies!
trying!to!cut!costs!while!maintaining!high!quality!products.!!
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4.0! Tasks!and!Activities!
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4.1!Researching!different!reverb!design!methods!
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•! Research!current!methods!of!creating!reverb!in!software!as!well!as!exploring!
cutting!edge!research!in!the!area.!
•! Explore!the!concept!of!combining!convolution!and!algorithmic!reverb!methods!
as!a!way!of!reducing!computational!requirements.!
•! Based!on!the!research!carried!out,!compare!each!method!of!reverb!and!
establish!a!shortlist!of!methods!to!investigate!in!further!detail.!
•! Design!or!find!from!existing!sources!examples!of!the!different!reverb!methods!
to!write!in!Matlab!to!put!forward!for!testing.!
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4.2!Comparing!the!Quality!of!Reverbs!
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•! Establish!a!minimum!reverb!quality!that!would!be!acceptable!for!use!in!a!piece!
of!consumer!gear.!
•! Through!research!of!existing!systems,!outline!the!resources!that!would!be!
available!for!reverb!in!terms!of!computational!power!and!memory!in!such!a!
product.!!!
•! From!existing!research,!devise!a!test!or!series!of!tests!that!will!allow!different!
reverb!algorithms!to!be!ranked!and!compared!objectively!in!terms!of!both!
“quality”!as!well!as!efficiency.!
•! Perform!the!test(s)!to!deduce!the!most!suitable!reverb!algorithm!for!use!in!an!
embedded!system.!
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4.3!Developing!and!Testing!a!Reverb!
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•! Using!existing!research,!explore!methods!of!improving!the!most!suitable!reverb!
to!make!it!more!efficient!and/or!to!improve!its!quality.!
•! Continue!to!test!the!reverb!as!it!is!altered!to!track!the!progress!of!efficiency!and!
quality.!
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5.0! Resources!
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The!resources!involved!in!this!project!are!generally!restricted!to!computers!and!
software,!however!as!a!way!of!applying!the!designed!reverb!to!an!embedded!system!
and!testing!its!performance,!it!would!be!useful!to!obtain!a!hardware!development!kit!
from!a!manufacturer!of!processors!for!audio!based!embedded!systems!such!as!
XMOS.!
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With!regards!to!software,!Matlab!would!be!the!most!suitable!application!to!design!and!
optimise!the!reverb!algorithms!as!it!is!a!good!platform!to!program!the!reverb!as!well!as!
getting!useful!data!back!when!performing!tests!on!the!performance.!To!test!the!reverb!
algorithms!in!a!simulated!embedded!system!environment,!the!software!
xTIMEcomposer!can!be!used!which!is!the!development!tool!for!the!XMOS!processor!
chip!technology.!
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6.0! Literature!Search!Methodology!
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The!literature!review!will!be!performed!by!using!a!variety!of!different!sources!both!
online!and!physical.!Online!papers!and!books!will!be!found!using!services!such!as!
Google!Scholar!and!the!BCU!Digital!Library.!Web!searches!will!also!be!used!to!find!
websites!with!useful!material,!as!well!as!finding!existing!products!or!systems!that!make!
use!of!different!reverb!techniques.!From!preliminary!research,!papers!from!the!DAFX!
conferences!or!books!about!digital!signal!processing!such!as!Smith’s!The'Scientist'and'
Engineer's'Guide'to'Digital'Signal'Processing'(Smith,!1997)!seem!like!they!would!be!
both!useful!and!reliable.!To!make!any!searches!efficient!and!to!ensure!the!most!useful!
resources!are!found,!keywords!and!phrases!will!be!used!to!optimise!the!search.!
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Possible!search!keywords/phrases:!
•! Reverb!
•! Realbtime!effects!
•! Embedded!systems!
•! DSP!effects!
•! Convolution!
•! Impulse!response!
•! Algorithm!
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Once!a!resource!has!been!found!using!search!engines!and!these!keywords,!they!will!
need!to!be!assessed!to!identify!their!relevance!and!quality.!The!relevance!of!a!piece!of!
work!will!be!assessed!by!first!reading!the!titles!and!creating!a!shortlist.!Then!from!the!
list,!the!abstracts!of!papers,!and!the!blurbs!and!introductions!of!books!will!be!read.!
This!will!give!an!idea!on!the!subject!matter!and!in!what!direction!the!piece!of!work!will!
take,!however!even!if!the!subject!matter!seems!like!it!will!be!of!some!use,!the!reliability!
and!quality!of!work!must!also!be!taken!into!account.!This!means!investigating:!
•! The!number!of!citations,!which!gives!a!very!quick!way!of!telling!whether!a!
piece!of!work!is!seen!as!good!by!the!academic!community.!If!it!has!been!cited!
in!many!other!people’s!work,!then!it!shows!that!those!people!considered!it!to!
be!a!trusted!piece!of!work.!A!new!piece!of!work!might!only!have!a!few!citations!
so!this!cannot!be!the!only!judge!of!the!quality.!
•! Whether!the!author!has!other!material!published,!and!the!overall!response!to!
it.!Establish!whether!the!author!has!any!professional!links!with!the!subject!area!
and!consider!any!potential!bias!this!may!introduce.!The!work!could!simply!be!
written!for!research!purposes,!or!instead!for!commercial!gain.!!
•! If!a!piece!of!work!has!few!referenced!sources!of!its!own!and!little!backing!up!of!
evidence,!it!is!possible!that!it!cannot!be!trusted!to!provide!accurate!information.!
•! The!target!audience!of!the!piece!of!work.!For!example,!if!the!work!is!presented!
for!middle!education!or!for!general!members!of!the!public,!it!is!possible!that!the!
work!has!been!oversimplified.!!
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Once!all!of!this!has!been!taken!into!account,!it!will!be!possible!to!decided!how!useful!(if!
at!all)!a!piece!of!work!will!be.!Both!the!relevance!and!reliability!of!work!can!be!graded!
using!a!scale!of!0!b!10!which!will!give!a!rough!order!to!approach!the!work.!A!document!
outlining!useful!sections!and!quotes!from!the!sources!will!be!created!using!software!
such!as!Evernote,!OmniFocus!or!Zotero,!where!appropriate!tags!can!be!applied!to!
allow!easier!navigation!when!revisiting!findings.!
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7.0! Schedule!
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A!common!method!of!planning!a!project!is!using!a!Gantt!chart.!It!displays!a!list!of!tasks!
or!events!over!time.!The!tasks!are!stretched!across!the!time!axis!to!give!an!indication!
of!when!they!should!be!beginning!and!ending.!More!detailed!Gantt!charts!can!give!
further!information!such!as!task!dependencies!and!links.!These!illustrate!the!work!flow!
of!the!various!tasks,!which!is!useful!to!visualise!how!certain!tasks!depend!on!other!
tasks!being!completed!before!any!work!can!be!started!on!them!for!example.!
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For!this!proposal,!a!fairly!simple!Gantt!chart!has!been!provided,!however!as!the!project!
matures,!a!more!detailed!Gantt!chart!can!be!created.!The!project!Gantt!chart!will!be!
kept!up!to!date!as!the!project!progresses,!identifying!any!previously!unforeseen!
changes!to!tasks!or!timings.!
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8.0! Risk!Assessment!
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This!project!requires!the!use!of!a!computer!for!almost!all!aspects!other!than!reading!of!
physical!material!so!one!of!the!main!risks!is!being!sat!at!a!computer!screen!for!too!
long.!Possible!problems!arising!from!this!include!posture!issues,!headaches!and!sore!
eyes.!This!can!be!managed!by!taking!regular!breaks!from!the!computer!while!working.!
Based!on!various!sources,!the!general!consensus!is!that!for!every!hour!of!work!a!
person!should!take!a!five!or!tenbminute!break!in!which!you!are!away!from!the!
computer!and!not!sitting!down.!
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Another!potential!hazard!is!listening!levels!when!testing!the!different!reverbs.!If!the!
listening!level!is!above!85dB,!permanent!damage!can!be!caused!to!the!auditory!
system!after!eight!hours,!with!the!exposure!time!decreasing!as!the!level!increases!
(World!Health!Organisation,!2015)!This!will!be!prevented!by!ensuring!that!listening!
levels!are!kept!below!85dB!or!if!they!go!above,!that!a!safe!exposure!time!is!
maintained.!
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9.0! Ethics!Review!
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Having!taken!the!online!ethics!test,!no!major!issues!arise!from!this!project!ethically.!
However,!from!the!risk!assessment,!one!of!the!potential!hazards!is!exposure!to!loud!
sounds!when!testing!different!reverbs.!Managing!this!hazard!will!be!of!paramount!
importance!if!playing!the!reverbs!to!third!party!listeners.!This!situation!could!arise!if!
performing!listening!tests!to!establish!the!“quality”!of!a!reverb.!
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10.0!References!
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Hurtig,!B.,!(1988)!Multi;Track'Recording'for'Musicians.!Alfred!Music.!
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Mike!Senior,!(2000)!Reverb';'Frequently'Asked'Questions.!Sound!on!Sound.!
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Smith,!S.W.,!(1997)!The'Scientist'&'Engineer’s'Guide'to'Digital'Signal'Processing,!1.!
ed.!ed.!California!Technical!Publ,!San!Diego,!Calif.!
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Valimaki,!V.!et!al.!(2012)!Fifty'Years'of'Artificial'Reverberation.!IEEE!Trans.!Audio!
Speech!Lang.!Process.!20,!1421–1448.!doi:10.1109/TASL.2012.2189567!
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White,!P.,!(2006)!Choosing'The'Right'Reverb.!Sound!on!Sound.!
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World!Health!Organisation,!(2015)!Make'Safe'Listening.'
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