Twenty Questions: Dynamic Details
Test your knowledge of compression in various applications
Go ahead and see how much you really know or don’t know about Compression.
This mini-test gets progressively more difficult and is a good indicator
of where you stand in this area of pro audio science.
In this issue, Rick Kreifeldt, Director of Engineering from dbx Professional
Products, has graciously guest authored a dynamics processing inspired
Twenty Questions.
There is one correct answer for each question. The answers are at the
bottom. Good luck!
1.) What does a Compression Ratio of 4:1 mean?
A.) Once past the threshold, the input signal must increase by 4dB for the output to increase by one dB.
B.) Once past the threshold, the output signal will be 4dB less than the input signal.
C.) Once past the threshold, the compressor will have 4dB of gain reduction.
Your Answer____________________
2.) Compressor attack time is defined as:
A.) The time it takes for the compressor to come out of gain reduction.
B.) The time it takes before the compressor starts gain reduction.
C.) The time it takes for the compressor to enter full gain reduction.
D.) None of the above.
Your Answer____________________
3.) Signals below the compressor threshold pass through without being compressed:
A.) True
B.) False
Your Answer____________________
4.) If a compressor is showing 10dB of gain reduction and you add 10dB of makeup gain, lower level signals below the threshold will be:
A.) Reduced by 10dB.
B.) 10dB louder.
C.) 20dB louder.
Your Answer____________________
5.) Signals below the threshold of a downward expander are:
A.) Passed through without any gain reduction.
B.) Reduced by the downward expander ratio.
C.) Made louder by the expansion ratio.
Your Answer____________________
6.) A soft knee compressor:
A.) Starts compression before the threshold.
B.) The compressor will not be at the full compression ratio until after the threshold.
C.) Has a lower output level at the threshold than a hard knee compressor.
D.) All of the above.
Your Answer____________________
7.) Gate attack time is defined as:
A.) The time it takes for the gate to enter gain reduction.
B.) The time it takes for the gate to close.
C.) The time it takes for the gate to come out of gain reduction.
D.) None of the above..
Your Answer____________________
8.) A parametric EQ with a bandwidth of 1/4 octave inserted into the side chain of a compressor with a boost of 6dB at 1 kHz will cause the compressor to compress a signal at 1kHz more than a signal at 100 Hz.
A.) True
B.) False
Your Answer____________________
9.) An optical compressor uses what for the gain element:
A.) Photo cell and LED.
B.) Photo diode and LED.
C.) Fiber optic VCA.
D.) Flux Capacitor.
Your Answer____________________
10.) A compressor is set to a 3:1 ratio. The threshold is set at +3dBu. If the input signal is at +12dBu, what is the level of the output signal?
A.) +4dBu.
B.) +5dBu.
C.) +6dBu.
D.) +7dBu.
Your Answer____________________
11.) A gate has a look-ahead time of 600uSec. Which of the following is true:
A.) The gate will open 600uSec faster if this feature is turned on.
B.) The gate looks 600uSec ahead in time to see if it will need to open.
C.) The gate will open in 600uSec plus the attack time.
D.) The main signal will be delayed by 600uSec so that the gate will have time to open before the signal passes through the gain element.
Your Answer____________________
12.) What will be the result of running the kick drum into the key input of the bassist’s gate?
A.) When the kick drum is played, the bassist’s sound will be compressed.
B.) The bass will only be heard when the kick is played.
C.) The bassist will finally be in time.
D.) The drummer will finally be on time.
Your Answer____________________
13.) An acoustic guitar player switches between strumming and finger picking in the same song. Which of the following compressor settings will make his finger picking 8 dB louder if his strumming peaks at 8dBu?
A.) Adjust the threshold to 8dBu and the ratio to 2:1.
B.) Adjust the threshold to 0dBu with a ratio of Infinity:1.
C.) Adjust the threshold and ratio until you have 8dB on the gain reduction meter when he is strumming and no gain reduction when he is finger picking. Add 8dB of make-up gain.
D.) Adjust the threshold 0dBu and the ratio to 8:1; add 8dB of make-up gain.
Your Answer____________________
14.) You are using a digital limiter. The A/D of the digital compressor reaches it’s maximum output when the input signal is at +22dBu, and the box is unity gain. Assuming no other gain through the unit, at what threshold must you set the digital limiter so that the output signal will not exceed +10dBu?
A.) 12dBFS
B.) +10dBFS
C.) +12dBFS
D.) 10dBFS
Your Answer____________________
15.) If a downward expander is set at a ratio of 1:1.5, a threshold of 40dBu, and a maximum attenuation or depth of 20dB, how much gain reduction will there be if the input signal is at 50dBu?
A.) 10
B.) 12.5
C.) 15
D.) 20
Your Answer____________________
16.) Compression ratio of 2:1. Compressor threshold of 10dBu. Limiter threshold of 0dBu. If the input signal is at +10dBu, how much gain reduction is being contributed by the limiter:
A.) 5dB
B.) 10dB
C.) 15dB
D.) 20dB
E.) None
Your Answer____________________
17.) If you want to duck music when someone talks into a mic, you should:
A.) Use a gate with the music going through the gate and the mic plugged into the key input.
B.) Use a mixer to add the two signals, and then use mixed signal into a key input of a gate.
C.) Use a compressor, with the music going though the compressor and the mic plugged into the side chain insert.
D.) None of the above.
Your Answer____________________
18.) A Hi-Shelf EQ is inserted into the side chain of a compressor. The EQ is set to cut 10dB at 5kHz with a slope of 18 dB/octave. The compressor is set to 2:1 at a threshold of -10dBu. If the input signal is +10dBu at a frequency of 10kHz, what is the level of the output signal?
A.) 5dBu
B.) 0dBu
C.) +5dBu
D.) +10dBu
Your Answer____________________
19.) Which compressor settings will most accentuate the transient attack of a snare drum?
A.) Fast attack and slower release.
B.) Fast release and slower attack.
C.) Fast attack, fast release, long hold time.
C.) 15dB
D.) Slow attack, slow release, short hold time.
Your Answer____________________
20.) Assuming you have a unit which is a multi-band compressor / limiter, which of the following statements is NOT true:
A.) A multi-way crossover is used to divide up the frequency bands.
B.) This unit can be used to de-ess full program material.
C.) For each band you have a separate VCA and RMS detector.
D.) Setting the threshold of each band’s limiter to 0dBu will ensure that the output will not be above 0dBu.
Your Answer____________________
Twenty Question Answers:
1.) A
2.) C
3.) A
4.) B
5.) B
6.) D
7.) C
8.) A
9.) B
10.) C
11.) D
12.) B
13.) C
14.) A
15.) C
16.) E
17.) C
18.) A
19.) B
20.) D
Guest quizmaster Rick Kreifeldt can be reached at rkreifeldt@dbxpro.com
September/October 2001 Live Sound International