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ATF 2 > Chapter 1 - Specifications > Flashcards

Chapter 1 - Specifications Flashcards

1
Q

What are audio specifications?

A

Audio specifications are specified by the manufacturer to give indication as to how a well a particular piece of equipment functions with regard to a particular purpose.

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2
Q

What is frequency response?

A

It is a measure of the magnitude and phase of the output as a function of frequency, in comparison to the input. represents how accurately a signal is reproduced by the system. When comparing the input signal to the output signal.

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3
Q

What is deviations with regards to frequency response? (Frequency Response: 0.35Hz – 200Khz +0/-3.0dB).

A

Deviation tells us how flat the frequency response is, the lower the number the better. But its importance depends greatly on the function of the device.

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4
Q

True or False. A Flat frequency response is desirable for audio amplifiers, reference monitors, and audio signal processors; but not necessarily in microphones or Hi-Fi speakers.

A

True.

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5
Q

What is Bandwidth?

A

Bandwidth gives us a more realistic idea of a piece of equipment’s frequency response as it only provides information for the area of the response that is used or produces power.

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6
Q

What specification indirectly tells you how noisy a unit is?

A

Signal to noise ratio.

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7
Q

What is signal to noise ratio (S/N ratio)?

A

It is the difference in dB between the maximum acceptable signal and any system noise that is present. The bigger the number the better.

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8
Q

What is Total Harmonic Distortion (THD)?

Example: THD: 0.008% typ

A

Total Harmonic Distortion, or THD, is a percentage of the overall signal composed of harmonic distortion. The smaller the number the better.

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9
Q

What is THD + Noise?

A

Similar to the THD test before, except instead of measuring individual harmonics this tests measures everything added to the input signal. This is a wonderful test since everything that comes out of the unit that isn’t the pure test signal is measured and included – harmonics, hum, noise, RFI, buzz … everything.

Example: THD+N: 0.01% typ

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10
Q

What is Intermodulation Distortion (IMD)?

A

A more meaningful test than THD, intermodulation distortion gives a measure of distortion products not harmonically related to the pure signal. This is important
since these artefacts make music sound harsh and unpleasant.
The lower the number the better

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11
Q

Consider the following specification:

IMD: 0.01% typ. SMPT

What is SMPT?

A

SMPT refers to the testing method. SMPT specifies this test use 60 Hz and 7 kHz combined in a 12 dB ratio (4:1).

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12
Q

Consider the following specification:

IMD: 0.01% typ. ITU-R

What is ITU-R?

A

The common test signal is a pair of equal amplitude tones spaced 1 kHz apart.
Nonlinearity in the unit causes intermodulation products between the two signals.
These are found by subtracting the two tones to find the first location at 1 kHz, then subtracting the second tone from twice the first tone, and then turning around and subtracting the first tone from twice the second, and so on.

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13
Q

What is crosstalk?

A

Signals from one channel leaking into another channel. This happens between independent channels as well as between left and right stereo channels, or between all
six channels of a 5.1 surround processor, for instance.

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14
Q

What signal is used to test equipment and provides equal energy across the reproducible audio spectrum?

A

Noise.

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15
Q

What are the two types of noise?

A

White Noise and Pink noise.

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16
Q

What is white noise?

A

White noise contains equal energy for every 1Hz band available.

Because the amount of 1Hz bands increase as octaves increase, it results in more energy gathering in the higher frequencies. This is why it sounds like high frequency hiss. This can be a problem when testing playback systems.

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17
Q

True or False?

Pink noise is used to test the internals of an audio system.

A

False. White noise is used to test the internals of an audio system. And is more useful for testing line amplifiers, signal processors & audio interfaces. Because of its linear form it is useful to test frequency response and filter curves within line level equipment. As it can provide a flat reference signal at the equipment’s input.

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18
Q

What is pink noise?

A

Pink noise is white noise that has been filtered using a 3dB per octave low pass filter. The filter is called a “pinking filter”. This produces a signal that contains equal energy per octave not equal energy per 1Hz Band.

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19
Q

What is pink noise used for?

A

This is used to test speaker systems that rely on the human ear as a reference.

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20
Q

What is Equivalent Input Noise? (EIN)

A

Output noise of a system or device referred to the input. This is generally how noise is specified on signal processors and audio mixers that have gain amps at the input, like the ones found on mic preamps.

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21
Q

What is dynamic range?

A

The maximum output voltage and then the output noise floor are measured and their ratio expressed in dB.

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22
Q

Which is correct?

a) Dynamic Range = 120 dB
b) Dynamic Range = 120 dB +26 dBu, 22 kHz BW

A

b

23
Q

What is Maximum Input Level?

A

The maximum input signal level in dBu that causes clipping or specified level of distortion.

24
Q

Consider the following:

Maximum Input Level = +20 dBu

What more information is needed?

A

Whether the applied signal is balanced or unbalanced and the amount of distortion or clipping used to establish the maximum must be stated. The preferred value is balanced and 1% distortion, but often manufacturers use “visible clipping,” which is as much as 10% distortion, and creates a false impression that the input stage can handle signals a few dB hotter than it really can.

Example: Maximum Input Level = +20 dBu, balanced, <1% THD

25
Q

What is maximum output level?

A

The unit’s output is measured to establish the maximum signal possible before visible
clipping or a specified level of distortion.

Correct: Max Output Level = +26 dBu balanced, 20-20 kHz, >2k ohms, <1% THD
Wrong: Max Output Level = +26 dBu

The manufacturer must state whether the spec is for balanced or unbalanced use
(usually balanced operation results in 6 dB more swing); what distortion was used for
determination (with the preferred value being 1% THD); over what frequency range is this
spec valid (prefer 20 Hz – 20 kHz; watch out for just 1 kHz specs); and what load
impedance is guaranteed (2k ohms or greater is preferred;

26
Q

What is Pro Audio Reference Level?

A

+4 dBu

27
Q

What is consumer reference level?

A

-10 dBu

28
Q

What units is slew rate commonly found on?

A

Amplifiers

29
Q

What is Slew Rate?

A

It is the rate of how quickly an amplifier can respond to a rapid change of input level. This is measured as a change in voltage with respect to time.

Slew rate has little to do with how an amplifier produces dynamics so much as its ability to effectively maintain output into higher frequencies.

30
Q

How do you measure a speakers sensitivity?

A

A microphone is placed 1 meter away from the speaker to measure the sound output (in decibels) with 1 watt of sound played through it.

31
Q

What is a speaker sensitivity?

A

Speakers’ ability to effectively convert power into

sound

32
Q

What does a speakers Power Handling Specification tell you?

A

How much heat a speakers voice coil can handle, measured in watts, without it incurring damage.

33
Q

How is average power determined?

A

Average power is derived from RMS voltage readings.

34
Q

How is peak power calculated?

A

Corresponds to the calculation of power based upon peak voltages. For a 6dB crest factor signal, peak power is four times the average power.

35
Q

What does PMPO stand for?

A

Peak Momentary Performance Output

36
Q

What is PMPO?

A

Trick question. The term PMPO has never been defined in any standard, but it is often taken to be the sum of some sort of peak power for each amplifier in a system. Loudspeakers are not designed to withstand their stated PMPO for anything but a momentary peak without serious damage.

37
Q

Name 5 causes of thermal speaker failure.

A 
• Too much average input signal.
• Excessive power outside of the
speakers bandwidth
• Amplifier clip
• Direct Current at the amplifiers output
(Uncommon)
• Excessive EQ on the outside of the
operational bandwidth
38
Q

As a general guideline, it is recommended to use an amplifier delivering ____% more power than the speaker’s average (“RMS”) power.

A

50%

For example, for a speaker with 450W average power, an amplifier with
an output of 700 - 900W may be used. If a small amplifier is used, a sufficient level will not be reached, nor the perception that it is attained, so the signal will tend to be clipped to compensate, thus endangering the integrity of the speaker.

39
Q

What is Impedance?

A

The opposition of electrical current flow within an AC circuit.

40
Q

Is audio AC or DC current?

A

AC

41
Q

What is Ohms Law? (equation)

A

V = IR

42
Q

What specification is important when matching amplifiers with speakers?

A

Impedance.

43
Q

Speakers with a _____ impedance can put strain on the power supply of an amp, if the amp can’t handle _____ impedance.

A

Low

44
Q

Choose the correct word.

In a series connection the impedances add/divide.

A

Add

45
Q

What happens if the load impedance is higher than the amplifiers rating?

A

More power is needed to drive the speaker, which would result in lower volume.

46
Q

Choose the correct word.

In a parallel connection, the impedances add/divide.

A

Divide

47
Q

What happens if the speaker impedance is too low?

A

Too much current will run through the amplifiers output transistors, causing the amplifier to overheat and shut down.

48
Q

Professional microphones should have a relatively low impedance of around ____.

A

150 Ohm

49
Q

Why is microphone impedance kept low?

A

Because a microphone’s generated AC current is very small and less resistance to the current would require less amplification.

50
Q

What does unmatched impedance cause?

A

Could cause echoes, or cause signals at certain frequencies to be reduced through cancellation.

51
Q

What impedance is line level today?

A

600 Ohms

52
Q

What is bridged impedance?

A

Use voltage matching instead. The idea here is to engineer the equipment to have the lowest possible output impedance and a relatively high input impedance — the difference between them must be at least a factor of ten, and is often much more.

53
Q

What do impedance matching transformers do?

A

They transform the signal to change its impedance.

ATF 2 (6 decks)

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