What is the steepest realistic audio transient in terms of V/us?

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#2
Assuming that the highest frequency you will ever see is 20kHz, the steepest transient would be for a full power 20kHz signal. The steepest part of the curve is at the zero crossing and is 2*pi*f*Vpk. So for a 100W/8ohms Vpk is 40V and the max transient would be about 0.5V megavolt/second or about 0.5V/usec.

Does that help?

Jan
 
#4
Op Amp Measurements: slewrate

-> NwAvGuy: Op Amp Measurements
Slew Rate – Here’s another huge myth: The faster the slew rate the better. But the fastest “slew” you can get from a 16/44 digital recording has a period of about 22 uS. So the O2, worst case, needs to slew 20 volts in 22 uS or a slew rate of 0.9 V/uS. And even considering those rare 24/96 recordings, the requirement is still 1.8 V/uS. SACD or 24/192, in theory, could require about 3.6 V/uS but, in practice, never will as that would be a 0 dBFS signal close to 100 Khz. Such a signal would never make it through the recording chain, and if it did, would fry tweeters and cause bats to fly into the side of your house. The peak levels in music generally fall as the frequency rises. This is especially true at ultrasonic frequencies. If you think I’m wrong, please reference a recording than can challenge even a 1.5 V/uS headphone amp.

The industry rule of thumb, even on the recording side of the signal chain, is 0.2 V/uS per volt RMS of maximum output. I’ve doubled that just to be ultra conservative so 7*0.4 = 2.8 V/uS for the O2’s requirement. As I have explained elsewhere,slew rates well in excess of what’s needed come at a price. Somewhere in the range of 2.5 – 5 V/uS is ideal for a high output headphone amp like the O2.
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#7
maty tinman said:
100 Wrms at 8 Ohms => 28.28 Vrms

28.28 x 0.2 = 5,6 Vrms/uS

28.28 x 0.4 = 11.3 Vrms/uS

With > 20 Vrms/uS I will do not have problem I think (orchestral music).

With 15 Vrms/us (LM3886 or LM4780) maybe (orchestral music).
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Yes you can always use a safety factor of course. But the question was what the fastest transient was, and that is about 5V/uS for 100W/8ohm.

Jan
 
#11
maty tinman said:
These numbers are with 20 Khz.

With 100 Khz => x5

28.28 x 0.2 = 5,6 Vrms/uS (20 Khz)

28.28 x 0.2 x 5 = 28 Vrms/uS (100 Khz)

This is why I do not want chipamps to play orchestral music.
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You a bat? Wanting to be able to output 100KHz at 100W is not really something anyone would want. Many prefer high slew rates as a belief and that's fine. But the music doesn't need it.
 
#15
maty tinman said:
These numbers are with 20 Khz.

With 100 Khz => x5

28.28 x 0.2 = 5,6 Vrms/uS (20 Khz)

28.28 x 0.2 x 5 = 28 Vrms/uS (100 Khz)

This is why I do not want chipamps to play orchestral music.
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Well, orchestral music or not, if you limit it to audio band, the 20kHz full level will determine your max transient 'speed'. I don't see why the type of music makes a difference?

Jan
 
#19
I seem to recall reading somewhere that the maximum slew rate actually seen with real music (not sure which genre) corresponds to that which you would see with a full amplitude sine wave at 2.2kHz. Hence if you design for 20kHz you have already built in a significant safety margin.

That 2.2kHz may have been from LP, so digital sources may need a bit more. Also, it was for music from an LP; scratches and dust will need more.

Anyway, the result is that slew rate is rarely the problem which some people imagine it to be. Attempting to solve a non-problem can often introduce much bigger problems.
 
#20
Amplifier Bandwidth

Amplifier Bandwidth
Audio Harmonics

However restricting high frequency about 20kHz (the theoretical limit of human hearing) assumes that the signals to be amplified are pure sine waves; In practice there is a trade off between a bandwidth wide enough to handle all the signals required, and a high frequency limit low enough to limit unwanted noise.

Most audio signals will be complex waves of many different and ever changing shapes. Audio signals are complex AC waves having fundamental frequencies in the range of 20Hz to 20kHz but also many higher frequency harmonics. To preserve the original shape of the signals (i.e. not introduce distortion) it is important that at least some of these harmonics are preserved. Therefore it is not advisable to sharply cut off the high frequencies at an arbitrary 20kHz, but rather allow some amplification of the apparently inaudible harmonic frequencies, which will contribute to the complex shape of the audible waves, especially where these signals contain sudden changes (fast transients) that require the presence of high frequency components to maintain their wave shape.

corrected-audio-response.jpg


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Orchestral music => fast transients

Amplifier bandwith != Audio bandwith
 
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