Several parameter issues of audio playback equipment

shaorc

【Ask if you don't understand】 I've seen some audio playback devices with the following parameter questions 【1】The audio response of a microphone, for example, is ±7dB (200Hz--10kHz). This means that within this frequency band, according to the formula 20lg(f1/f0), the calculated value is within ±7, right? 【2】Continuing with the question, which of the above values do the values of f1 and f0 refer to, and how do I choose? 【3】The preamplifier output level parameter is ±3dB (2V). According to the formula 20lg(u1/u0), the calculated value is within ±3, right? Does 2V refer to U1 or U0? 【4】For example, in a broadcasting device with a microphone, when a person makes a sound (analog signal), it is received by the microphone and then immediately converted to digital through the chip inside the device. However, human voices have different pitches and frequencies. If the sound is shouted, will the amplitude of the audio analog input be too high? This is common in walkie-talkies and microphones, but I don’t know the principle.

maychang

【1】For example, the audio response of a microphone is ±7dB (200Hz--10kHz). Does this mean that within this frequency band, according to the formula 20lg(f1/f0), the value calculated is within ±7? It is not the ratio of two frequencies, but the ratio of two voltages. The two voltages are: one is the voltage in the middle of the frequency response (in this section, the voltage gain changes very little with frequency), and the other is the voltage at 200Hz or 10kHz. In addition, this is not the frequency response of the amplifier, but the frequency response of the microphone.

maychang

For example, in a broadcasting device with a microphone, a person makes a sound (analog signal), which is received by the microphone and then immediately converted to digital through the chip inside the device. Generally, it is amplified first. If you want to perform analog-to-digital conversion, you should also amplify the microphone output signal to a level suitable for analog-to-digital conversion before converting it. Moreover, very few audio devices need to perform analog-to-digital conversion on analog signals (such as microphone output), and they are usually amplified directly.

chunyang

In the definition of microphone frequency response, the dB value refers to the output level range, that is, the frequency range that the microphone can respond to within a specific output level range. Beyond this frequency range, the microphone's output level will be lower than a certain limited intensity, and it is considered to be beyond the frequency response range. During the test, a sound source with a constant sound pressure is given, and then the frequency of the sound source is changed, and the microphone output level is observed. If the change does not exceed ndB, the microphone frequency response at this dB value is considered to be xxHz-yyHz.

shaorc

maychang published on 2019-4-4 12:49 [1] The audio response of the microphone, for example, the parameter is ±7dB (200Hz--10kHz), which means that within this frequency band, according to the formula 20lg(f1/f0), the calculated value is...

It is not the ratio of two frequencies, but the ratio of two voltages. The two voltages, one is the voltage in the middle of the frequency response (in this section, the voltage gain changes very little with frequency), and the other is the voltage at 200Hz or 10kHz. So my formula should be modified to 20lg(u1/u0), [1] One voltage is the voltage in the middle of the frequency response (in this section, the voltage gain changes very little with frequency), which voltage refers to U1 or U0? What does this middle section refer to? [2] Is a voltage of 200Hz or 10kHz? Is this U1 or UO? Should I choose the 200Hz voltage or the 10kHz voltage? [3] Whether it is the frequency response of an amplifier or a microphone, does "frequency response" refer to the ability of an electrical appliance to process signals (output effect) within a certain frequency band?

maychang

shaorc posted on 2019-4-4 14:02 It is not the ratio of two frequencies, but the ratio of two voltages. Two voltages, one is the voltage in the middle of the frequency response (in this section, the voltage gain changes very little with frequency)...

[1] One voltage is the voltage in the middle of the frequency response (in this section, the voltage gain changes very little with frequency). Does this voltage refer to U1 or U0? What does this middle section refer to? It refers to u0. The middle section is the section with a flat frequency response. The gain basically does not change in this frequency range.

maychang

shaorc posted on 2019-4-4 14:02 It is not the ratio of two frequencies, but the ratio of two voltages. Two voltages, one is the voltage in the middle of the frequency response (in this section, the voltage gain changes very little with frequency)...

[2] One voltage is 200Hz or 10kHz, is this U1 or UO? So should I choose the voltage of 200Hz or 10kHz? It is neither 200Hz nor 10kHz. You might as well take the midpoint of 200Hz and 10kHz, 1414Hz.

maychang

shaorc posted on 2019-4-4 14:02 It is not the ratio of two frequencies, but the ratio of two voltages. The two voltages, one is the voltage in the middle of the frequency response (in this section, the voltage gain changes very little with frequency)...

[3] Whether it is the frequency response of an amplifier or a microphone, "frequency response" refers to the ability of the appliance to process signals (output effect) within a certain frequency band. It means that the gain of 200Hz is reduced by 7dB relative to around 1414Hz, and the gain of 10kHz is reduced by 7dB relative to around 1414Hz.

shaorc

maychang posted on 2019-4-4 15:12 【3】Whether it is the frequency response of an amplifier or a microphone, "frequency response" refers to the ability of an electrical appliance to process signals within a certain frequency band (output efficiency...

Oh, this is called frequency response. Response does not refer to the reception response or reaction that we usually sayBy the way, when does the capacitor play a role in isolating DC, and when does the capacitor play a role in delay? For example, in the figure below, I always thought that C2 and C3 were used to isolate DC VCC, so I couldn’t analyze the following circuit clearly. It turns out that the capacitor here cooperates with the resistor to play a role in delay (because the capacitor is charged) However, connecting a capacitor from the power supply to the ground or to the base of the transistor plays the role of bypass and decoupling, which is the role of isolating DC

maychang

shaorc posted on 2019-4-4 15:41 Oh, this is called frequency response. Response does not refer to the reception response or reaction as we usually say.

Oh, this is called frequency response. Response does not refer to the reception response or reaction as we usually say. "Heavy metal" means metal with relatively high density in physics, metal with large atomic number in chemistry, and a performance style in rock bands.

shaorc

maychang posted on 2019-4-4 15:46 Oh, this is called frequency response. Response does not refer to the reception response or reaction as we usually say. "Heavy metal" means density in physics...

Oh, that's it. I just edited the reply on the 9th floor and have another question. Please take a look

maychang

shaorc posted on 2019-4-4 15:50 Oh, that's it. I just edited the reply on the 9th floor and have another question. Please take a look.

It's hard to say. It still needs specific analysis of specific situations. It can't be generalized that what is connected to a certain place must have a certain function.

shaorc

maychang posted on 2019-4-4 16:01 It's hard to say. We still need to analyze the specific situation, and we can't generalize that what is connected to a certain place will have a certain effect.

For the figure on the 9th floor, as shown below, the VCC from C2 through R4 and R5 is delayed, because it is slower than the route from VCC to C3 and then to R3, making Q3 conduct before Q2. But the capacitor isolates the DC, so for the route from C2 through R4 and R5, shouldn't VCC be blocked (cannot pass C2)?

maychang

shaorc posted on 2019-4-4 16:21 For the figure on the 9th floor, as shown below, VCC is delayed from C2 through R4 and R5, because it is faster than from VCC to C3 and then to R3...

Specifically in this figure, C2 is still used for delay. It's just that when the OUT terminal is short-circuited to the ground, C2 is charged through R4. After the voltage across C2 rises, Q2 is turned on and Q3 is turned off.

shaorc

[quote]maychang published on 2019-4-4 17:31 Specifically in this figure, C2 is still used for delay. It's just that when the OUT terminal is short-circuited to the ground, C2 is charged through R4. After the voltage across C2 rises, Q2 is turned on, and Q3 is turned off. When OUT is short-circuited to the ground, R5 is already short-circuited and is considered to be gone. At this time, Q3 is turned on. Why does VCC need to be charged through C2 and R4? At this time, Q3 is turned on, and R5 is gone, which means that the rightmost vertical path has no impedance. Why doesn't the current forget to go here, and also charge C2? After Q2 is turned on, the electricity on C3 is discharged through Q2 and R3, causing Q3 to be turned off?

maychang

shaorc posted on 2019-4-4 17:52 It's just that when the OUT terminal is short-circuited to the ground, C2 is charged through R4. After the voltage across C2 rises, Q2 is turned on and Q3 is turned off. When OUT is short-circuited to the ground, at this time...

When OUT is short-circuited to the ground, R5 has been short-circuited and is considered to be non-existent. At this time, Q3 is turned on. Why does VCC need to be charged through C2 and R4? You have already said: R5 is equal to non-existent, so the OUT terminal is equal to the ground potential, and VCC is obviously charged through C2 and R4. Note that Q3 cannot be equal to a short circuit at this time. The base current of Q3 cannot be arbitrarily large due to the limitation of R3.

maychang

shaorc posted on 2019-4-4 17:52 It's just that when the OUT terminal is short-circuited to the ground, C2 is charged through R4. After the voltage across C2 rises, Q2 is turned on and Q3 is turned off. When OUT is short-circuited to the ground, at this time...

After Q2 is turned on, the electricity on C3 is discharged through Q2 and R3? Cause Q3 to be cut off? Q2 is turned on, causing C3 to discharge (the voltage across Q2 is only around 0.2V or even less), and Q3 is turned off.

zhuyebb

Pure friendly support

shaorc

maychang published on 2019-4-4 18:03 When OUT is short-circuited to ground, R5 is short-circuited and regarded as non-existent. At this time, Q3 is turned on. Why does VCC need to be charged through C2 and R4? You have already said: R5 is equal to non-existent.

R5 is equal to ground potential, so OUT is equal to ground potential. VCC is obviously charged through C2 and R4. Note that Q3 cannot be equal to short-circuit at this time. The base current of Q3 cannot be arbitrarily large due to the limitation of R3. Oh, you mean when OUT is short-circuited, it is directly connected to the ground, and R5 is considered to be gone. Q3 is not in a short-circuit state at this time, so VCC will not be directly short-circuited from Q3 to the ground. Then there are two questions: [1] Why is it that only VCC charges C2 through R4 at this time? But VCC does not charge C3 through R3? [2] When the output OUT is short-circuited, Q3 is not in a short-circuit state, so what is the state?

maychang

shaorc posted on 2019-4-5 09:28 If R5 is equal to nothing, then the OUT terminal is equal to the ground potential, and VCC is obviously charged through C2 and R4. Note that Q3 is not equal to a short circuit at this time, and the base current of Q3 is...

[1] Why is it that only VCC charges C2 through R4 at this time? But there is no VCC charging C3 through R3? The initial state of the circuit is that Q3 is on and Q2 is off. C3 has been charged through R3 to the point where Q3 is turned on, while C2 is charged very little (not enough to turn on Q2) because Q3 is turned on (the potential at the OUT terminal is close to the power supply potential). Now the circuit is reversed, and it is obvious that one of C2 and C3 is charged and the other is discharged.