The Black Box - Report

8/12/2019 The Black Box - Report

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The Black Box

Eric Moskus

&

Nathan Sibon, Zach Bruin, Josh Roberts, Chris Nottoli, Melissa King

November 2th, 2!"#

$coustical %esting '(r) (omini*ue Ch+enne

(r) auren Ronsse

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Abstract:

%he ob-ective o. The Black Box /as to accuratel0 1escribe the comonents containe1 insi1e o. a

locke1 case, using an0 available e*uiment) %he case itsel. containe1 t/o inuts 3labele1 4C5 an1 4(56

an1 t/o oututs 3labele1 4$5 an1 4B56) t /as .oun1 that bet/een inut 4C5 an1 outut 4B5 /as a

grahic e*uali7er, a 1o/n/ar1 e8an1er /ith a 9'" ratio, an1 a comressor:limiter /ith an ;'" ratio

an1 a threshol1 at 6 inter.erence an1 noise into that outut) nut 4(5 /as entirel0 1isconnecte1 .rom the

signal chain /ithin the case)

Introduction:

The Black Box /as the last o. three ro-ects to be comlete1 .or the $coustical %esting course

at Columbia College Chicago) %he aim o. the ro-ect /as to accuratel0 1escribe the comonents

containe1 insi1e o. a locke1 case 3herea.ter re.erre1 to as, 4the black bo856)

Initial Listening Tests:

%he black bo8 3icture1 in >ig) "6 has t/o inuts 34C5 an1 4(56 an1 t/o oututs 34$5 an1 4B56)

nitial listening tests /ere con1ucte1 to 1etermine the .un1amental connections bet/een each inut an1

outut) ?arious signals 3sine tones, /hite noise, etc)6 /ere generate1 .rom a %erraSon1e $u1io %oolbo8

3icture1 in >ig) $


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%hese listening tests reveale1 that the onl0 /orking connection /as bet/een inut 4C5 an1

outut 4B5) $ subse*uent listening test using music as a source also reveale1 /hat soun1e1 like a noise

gate bet/een inut 4C5 an1 outut 4B5) =nl0 the transients an1 lou1est sections o. the music /ere

outut .rom the lou1seaker)

Regar1less o. inut, the outut o. 4$5 /as onl0 noise, an1 the original signal being sent in .rom

the lou1seaker /as lost) t /as notice1, ho/ever, that a sine tone la0e1 through inut 4C5 coul1

.aintl0 be hear1 over the nois0 outut o. 4$5) %his onl0 occurre1 using high outut levels o. the $u1io

%oolbo8) %his /as believe1 at the time to be an e..ect o. crosstalk bet/een the channels)

hen the onl0 inut use1 /as 4(5 no signal coul1 be hear1 out o. 4B5, an1 4$5 onl0 outut its

characteristic noise) >rom the listening tests it /as believe1 inut 4(5 /as not connecte1 to the signal

chain /ithin the black bo8)

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Fig. 1: Image of the black box with inputs "C" and "D" and outputs "A" and "B". he powe!suppl is located on the left.


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Output A:

nitial listening tests 1emonstrate1 that the outut o. 4$5 /as noise) %o better un1erstan1 the

*ualit0 o. that noise, a series o. nine 1i..erent .re*uenc0 resonse grahs /ere constructe1 .rom inut

4C5 an1 4(5 to outut 4$5, using the %E>2! unit an1 Soun1 ab so.t/are) Each .re*uenc0 resonse

test /as er.orme1 at a slightl0 higher outut level than the revious, so that the variation o. .re*uenc0

resonse over amlitu1e coul1 be observe1) >ig) 2 sho/s the overla0 o. these nine searate .re*uenc0

resonse grahs)

9

Fig. 2: Pictured is an overlay of nine separate frequency response graphs over varying amplitude, from inputs ! and "

to output !. #reated using the T$F2% unit and &ound 'a( soft)are. The output kno( on the T$F2% unit )as used to

increase the amplitude for each of the nine tests. $ach frequency response )as then overlayed to create this graph. The

imprecise method of turning the kno( means that the difference in amplitude for each test is different. !mplitude levels onthe y*axis of graph )ere not cali(rated and can only (e used in relative terms. +verall, the graph sho)s little variation in

frequency response )ith changing amplitude. t also sho)s several distinct peaks in frequency response -% /0, 1% /0,etc.3. Parameters used during these tests can (e seen in Ta(le B*1 in !ppendix B.


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%he small variation in .re*uenc0 resonse .or var0ing amlitu1es that is seen in >ig) 2 in1icates

that outut 4$5 is largel0 in1een1ent o. inut level) t /as also believe1 that the .re*uenc0 resonse

eaks 3beginning /ith a eak aroun1 ! D76 ma0 have been a result o. groun1 hum or R> inter.erence

.rom comonents in the surroun1ing room) %he crosstalkig) $ /as transmitte1 into the

black bo8) %he signal generator 3icture1 in >ig) $ signals coul1

be broa1cast an1 1emo1ulate1 on outut 4$5, roving that it /as acting as an antenna, an1 /as

constantl0 icking u R> inter.erence on its channel) >ig) 9 sho/s the transmitte1 signal being imose1

on the noise o. outut 4$5)

G

Fig. 4: &ignal chain used during the radio transmitter tests. t represents t)o physically isolated signal chains. /o)ever,

the antenna of the radio transmitter )as placed almost directly against the (lack (ox.


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From Input to Output B:

Fre!uenc" #esponse:

Fsing a %E>2! unit 3see >ig) $


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>ig) # sho/s all the characteristic .re*uenc0 resonse eaks an1 1is o. an e*uali7er) t /as also

1etermine1 that each eak an1 1i correson1e1 closel0 /ith


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%o construct the trans.er .unction grahs, the level o. the 1irect, re.erence signal .rom the signal

generator /as incrementall0 increase1 b0 )G 1B?, an1 the correson1ing voltage o. the signal through

the black bo8 /as recor1e1 at each increment) %hese oints /ere then lotte1 an1 the rocess /as

reeate1 .or a total o. eight 1i..erent .re*uencies) %he0 are all overla0e1 an1 grahe1 in >ig) G)

%he trans.er .unction grah in >ig) G sho/s the amlitu1e


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on the 1i..erent .re*uencies)

t /as also notice1 that lo/ .re*uencies aeare1 to be sub-ect to a higher limiter threshol1 than

that .or higher .re*uencies) >or instance, >ig) G sho/s that the limiter .lattens high .re*uencies to

aroun1 ig) G also hele1 e8lain /h0 it soun1e1 as i. there /as a noise gate bet/een

inut 4C5 an1 outut 4B5 1uring the listening tests) $ consistent sloe o. .our /as calculate1 .or the

1i..erent .re*uencies, as the0 rise .rom the noise .loor to the oint /here the0 hit the limiter threshol1

3as seen in >ig) G6) $ 1o/n/ar1 e8an1er, /orking at a "'9 ratio, e8lains the consistent sloe o. the

lines in >ig) G, as /ell as the soun1 o. the noise gate 1uring listening tests) t /as also 1etermine1 that

the 1o/n/ar1 e8an1er threshol1 must be at or above the comressor threshol1, because the

1o/n/ar1 e8an1er /orks on the signal at ever0 oint bet/een the noise .loor an1 limiter threshol1)

%ignal Flo&:

%he signal .lo/ o. comonents in the black bo8 /as con.ine1 to being bet/een inut 4C5 an1

outut 4B5) %his is because outut 4$5 /as 1etermine1 to be acting as an antenna, an1 inut 4(5 /as

1etermine1 to be entirel0 1isconnecte1 .rom the signal .lo/) %he grahic e*uali7er /as 1etermine1 to

be the .irst comonent bet/een inut 4C5 an1 outut 4B5) . the grahic e*uali7er came a.ter the

1o/n/ar1 e8an1er then the lines o. sloe .our seen in >ig) G /oul1 not have been consistent) . the

grahic e*uali7er came a.ter the limiter then the e*uali7ation shoul1 retain its shae a.ter the limiter

"!


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threshol1 is reache1, though >ig) # sho/s that this is not the case)

t /as also 1etermine1 that a shelving EA /as the last comonent in the signal chain because it

/as believe1 to have raise1 lo/ .re*uenc0 content over the limiter threshol1) %he or1er bet/een the

1o/n/ar1 e8an1er an1 limiter coul1 not be 1etermine1) %he actual signal .oun1 insi1e the black bo8

is sho/n in >ig) )

>ig) sho/s that there /as no shelving e*uali7ation a.ter the limiter bet/een inut 4C5 an1

outut 4B5) %he higher limiter threshol1 at lo/ .re*uencies 3as observe1 in >ig) # an1 >ig) G6 /as

actuall0 1ue to an ime1ance mismatch bet/een s0stems, an1 coul1 have been reme1ie1 /ith the use

o. a resistor in the signal ath)

$s re1icte1, the shae o. the grahic e*uali7er resemble1 the shae o. the e*uali7ation seen in

>ig) #) %he ratioHs .or both the 1o/n/ar1 e8an1er an1 the limiter /ere accuratel0 .oun1) Do/ever, the

actual threshol1 o. the limiter 3


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onclusion:

%hrough a series o. various tests, the comonents insi1e o. the black bo8, as /ell as the basic

settings .or those comonents, /ere .oun1) t /as 1etermine1 that bet/een inut 4C5 an1 outut 4B5

/as a grahic e*uali7er, a 1o/n/ar1 e8an1er /ith a 9'" ratio, an1 a comressor:limiter /ith an ;'"

ratio an1 a threshol1 at 6 inter.erence an1 noise into that outut) nut 4(5 /as entirel0 1isconnecte1 .rom the

signal chain /ithin the case)

Several e8tra tests coul1 have been er.orme1 to attain greater accurac0 in results) . the

electrical ime1ance o. the 1evices ha1 been consi1ere1 then the mistaken claim o. a shelving

e*uali7er coul1 have been avoi1e1, an1 the lo/ .re*uenc0 s/ell in resonse at high amlitu1es coul1

have been negate1) n turn, this /oul1 have allo/e1 the threshol1 o. the comressor to be calculate1

more accuratel0) %he attack time o. the limiter coul1 also be calculate1 b0 sen1ing imulses o. various

lengths into the black bo8) . an imulse b0asses the limiter then its 1uration is shorter than the attack

time o. the comressor) %he length o. the imulse coul1 then be increase1 until it is caught b0 the

limiter, an1 this length /oul1 be the attack time o. the limiter)

"2


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Appendices

Appendix A ' (ictures o$ %etup and )!uipment

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Fig. !*2: Pictured is the signal generator and millivoltmeter used primarily in constructingthe transfer function graphs seen in Fig. 9. The red line on the millivoltmeter -on the left3represents the level of the the 1k/0 tone through the (ox )hile the (lack line on the

millivoltmeter -on the right3 represents the dry, reference signal directly from the signal

generator.

Fig. !*1: Pictured is the Terra&onde !udio Tool(ox, )hich )as used to generate different types

of signals -sine )ave, )hite noise, etc.3 for various tests. The T$F2% unit is also pictured. t )as

used to generate the frequency response graphs seen in Fig. 2 and Fig. 4.


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Appendix B ' Fre!uenc" #esponse (arameters

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Ta(le B*1: Frequency response parameters used to construct the frequency

response graphs seen in Fig. 2 and Fig. 4. !ll parameters )ere kept the same for

each test, and all tests performed )ith the T$F2% unit in the &ound 'a(

soft)are.

Start Frequency: 20 Hz

Stop Frequency: 20,000 Hz

Sweep Time: 59.733 s

Sweep Rate: 33.5 Hz!s

Frequency Reso"ution: #$.3 Hz

Time Reso"ution: 5.%$ ms

&istance Reso"ution: %#.79 'eet(an)wi)t*: #$.3 Hz

+umer o' Samp"es: $#92

Frequency Response Parameters

Fig. !*4: This is a picture of the radio transmitter used to transmit sine tones into

output !. The transmitter unit utili0es an

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