Here is the schematic for the RF amplifier circuit of Lab For some circuits the transient response is more important. For example, consider the CMOS inverter:. Select Edit Instance Model Text :. Here we have. Do the same for the PMOS transistor. Now we will do a DC sweep rather than an AC sweep. Sweep source V2 from 0V to 5V at 0. Email Required, but never shown. Featured on Meta. Related 0. Hot Network Questions. Viewed 16k times. You say "how would I be able to isolate the frequency and show it at each point in time?
In other words, there is no frequency value that uniquely corresponds to each point in time or, at least, you can't derive that information from the time-domain data. If you could, you would be violating the Heisenberg uncertainty principle. Oliver Charlesworth Oliver Charlesworth k 25 25 gold badges silver badges bronze badges. In addition, if the system is time-invariant so LTI , then the frequency response also will not vary with time. Thus for LTI systems, the frequency response can be seen as applying the system's transfer function to a purely imaginary number argument representing the frequency of the sinusoidal excitation.
For an audio system, the objective may be to reproduce the input signal with no distortion. That would require a uniform flat magnitude of response up to the bandwidth limitation of the system, with the signal delayed by precisely the same amount of time at all frequencies. That amount of time could be seconds, or weeks or months in the case of recorded media. In contrast, for a feedback apparatus used to control a dynamic system, the objective is to give the closed-loop system improved response as compared to the uncompensated system.
The feedback generally needs to respond to system dynamics within a very small number of cycles of oscillation usually less than one full cycle , and with a definite phase angle relative to the commanded control input. For feedback of sufficient amplification, getting the phase angle wrong can lead to instability for an open-loop stable system, or failure to stabilize a system that is open-loop unstable.
Using analysis techniques similar to those used for the low pass filter, it can be shown that. Therefore this circuit is a high-pass filter it passes high frequency signals, and blocks low frequency signals.
Besides low-pass filters, other common types are high-pass passes only high frequency signals , band-reject blocks certain signals and band-pass rejects high and low frequencies, passing only signal areound some intermediate frequency.
The simplest band-pass filter can be made by combining the first order low pass and high pass filters that we just looked at. However, this circuit cannot be used to make a filter with a very narrow band. To do that requires a more complex filter as discussed below. These quantities are shown on the diagram below. What does this mean in the real world? Audio content timing errors tend to occur more with low bit rates, and the effect is particularly noticeable on the human voice.
Audio files G-I demonstrate that pre-echoes and roughness are easily heard in the sound of applause:. Pay attention to the foreground the loud, obvious claps and the background the details of the unfocused individual claps. Audio Example I: At 64kbps, this is an extreme example, but it's actually not uncommon when watching downloaded videos or YouTube-type material.
The temporal displacement and time-smearing results in audible ringing at different frequencies. Bear in mind that this bit rate is higher than in the formats offered by many streaming multimedia sources. On Now Now Sleepyhead's track 'Milestones', which I've used as an example, the following differences can be heard:. Lacking crispness, punch and bite, it sinks back into the mix, behind the vocals.
The transparency, clarity, and energy is changed. See audio examples L and M referenced above. The AAC format fares much better in bass resolution, and it is thus much more forgiving to the bass. Because perceptual audio coding schemes remove frequency content, our masking perceptions and our sense of the amplitude of the remaining frequency content can be changed.
The energy and dynamic range of some sounds can be attenuated or compressed. When frequency content is smeared over time, its average level over time increases slightly.
This can result in the listener perceiving it as louder, with further consequences for timbre and frequency masking. Audio Example Q: spaced test tones. Image 11 shows high-frequency content missing red arrows : hot colours which represent greater amplitudes are either missing in the output of the compressed format or smeared and less precise green, blue and black arrows.
Generally, the hot-coloured frequency content shapes of the original are less clear in the compressed format, and we can see that the time and amplitude components of the material have been changed. Another common artifact, commonly referred to as 'swirlies', is caused by the rapid coming and going of lower-level frequency content in the compressed format, which is stable in the raw file.
Pay close attention to the hi-hat and cymbals throughout the excerpt, and the sibilant consonants of the vocal, all of which are consistent and smooth. The vocals, and indeed the entire mix, is flat, lifeless, and lacks clarity and definition. Perceptual coding relies on our ears' inability to hear frequency content obscured by other frequency content.Frequencies for equal-tempered scale, A 4 = Hz Other tuning choices, A 4. Speed of Sound = m/s = ft/s = miles/hr.