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  • fader结束音量为curVolumDb + attuationDb,那么fader结束的gain值为:endGain = dbToGain(curVolumDb + curVolumDb) 将fader的开始到结束的时间timeMs转化为sample为单位:timeInSample = timeMs * sampleRate / ...

    原文链接:http://www.cnblogs.com/fellow1988/p/9589261.html
    fader在音频处理中是比较基础的处理。通常用于平滑的调节音量,或是音频的渐入和渐出效果。

    比较常见的fader有line和cubic线型的fader。

    line fader即fader的渐变过程是线性的。cubic的渐变过程是三次曲线。

    fader主要有三个参数,attuationDb, type, timeMs.

    line fader:

    通过当前的音量curVolumDb,计算fader的初始gain值:startGain = dbToGain(curVolumDb)

    fader结束音量为curVolumDb + attuationDb,那么fader结束的gain值为:endGain = dbToGain(curVolumDb + curVolumDb)

    将fader的开始到结束的时间timeMs转化为sample为单位:timeInSample = timeMs * sampleRate / 1000.

    那么line fader的step为:step = (endGain - startGain) / timeInSample.

    初始化curSample为0, curGain= startGain.

    每处理一个sample(sample * curGain), curSample加1. curGain加step,直至curSample等于timeInSample,整个fader过程结束。

    5s内衰减5db

    在这里插入图片描述

    5s时间fader in

    在这里插入图片描述

    cubic fader:

    cubic fader的原理为,将0~1划分为多个段(假设为segNum)。计算每个Segment端点的gain值:segGain.

    由于有segNum个段,那么0~1被离散为segNum + 1个点,每个点的segGain[n]值为(n/(segNum +1))^3. n=0,1,2…segNum+1;

    将0~1之间的segGain map到startGain ~ endGain之间。

    对于0~timeInSample之间的点,我们计算当前的sample处于哪个segment,当curSample是当前segment的第一个点时,将curGain设置成segGain[n].

    当前segment按line fader一样的方法计算每个点的gain,每处理一个sample, curGain加step.

    5s内衰减5db

    在这里插入图片描述

    5s时间fader in

    在这里插入图片描述

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  • Image via fender.com当你在排练或演出时想要让自己的音箱更大声些,抱着这个无比单纯美好的目的,走向音箱时,结果发现上面N个旋钮上豁然写着“gain”、“trim”、“level”、“volume”、“master”…眼都看花了,...

    fab0f126527866e8bf4b93148854795e.gif

    Image via fender.com

    当你在排练或演出时想要让自己的音箱更大声些,抱着这个无比单纯美好的目的,走向音箱时,结果发现上面N个旋钮上豁然写着“gain”、“trim”、“level”、“volume”、“master”…眼都看花了,如果你是天秤座,这个时候肯定阵亡。我们先不急着去逐个比较,因为这其中最基本的两组参数也在很多人心中存疑。能区分开Gain(增益)和Volume(音量)后,相信在实战中你能更好地驾驭吉他音箱。

    Gain/增益

    用最简单的方式来解释,增益用来增强输入进音箱电路的信号。通常我们调试增益参数的过程就是在前级区域内调试输入信号的强弱。也就是说,增益控制的是设备的“输入”一端。

    Volume/音量

    音量影响的是后级最终输出的响度。不管对于吉他箱来说还是贝司箱,都是一样的。不管是音箱接上了效果回路还是有AUX发送,最后控制输出的Volume/音量参数都会对其产生影响。

    增益和音量的关系

    增益多与“敏感度”相关,比方说:你的麦克风需要更“灵敏”吗?那么就把增益开大些。但是增益开得过大,信噪比会降低,底噪声就会更加明显。还会因电流输出限制产生削波失真。 这就是我们所说的“过载”效果的真正来源。也是很多朋友想要通过开大clean通道的volume去制造过载却不明显的原因。

    如果把增益开大,把音量关小的话,可以得到过载的效果。很多60,70年代的音乐作品中可以听到这种音色;关小增益开大音量的话,音符会很清晰,颗粒性也很好。

    关于增益和音量的设定

    调节音箱的时候应该从增益旋钮开始,如果增益旋钮不起作用的话,说明以前曾经输入过大的信号,增益功能已经闭锁了。而且如果“峰值(Peak)”灯一直亮着的话,会引发音箱的故障。使用真空管音箱的时候,如果增益的数值过大的话,可以发出失真的音色。有些吉他手或贝司手喜欢这种音色,但是对于音箱的负担过大,不利于音箱的保养。而且有些输出功率本来就很小的音箱,偏要输入巨大的信号的话,会引发音箱的故障。

    以下是一些具体的操作窍门:

    1.调节增益的时候要注意和音量的配比:开始就要把音量开到一定的程度。如果把音色都调节好,再开音量的话,音色会有一些变化。

    2.把EQ的所有数值调到中间值,然后把增益和音量调到12点的位置。这时候二者的平衡应该处于很好的状态。

    3.如果音色发生失真,可以更换一个输入插口,或打开-15dB开关。

    4.对于贝司手来说:如果使用的是主动贝司,但音色一点没有力度的话,可以尝试插入被动插口。

    5.如果音箱发出的音色依旧很小,可以尝试在接入音箱之前加入激励器等提高信号的效果器。

    6.找到了合适的输入水平之后,再把音量调节到合适的大小。大家可以尝试左手调节增益旋钮,右手调节音量旋钮,把两个旋钮向反方向旋转,从而找到合适的音量。因为把增益开大,把音量关小,和关小增益开大音量的效果完全不相同

    7.如果找到自己满足的声音的话,就没有必要再调节EQ了,因为EQ主要起到对音色修饰的作用。

    8.如果峰值灯亮的话,不要把增益开得过大。如果没有开大之前声音就发生失真的话,打开-15dB开关。

    更多资讯可关注“音平资讯”微信号,扫描下图轻松添加。

    fab0f126527866e8bf4b93148854795e.gif

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  • Abstract: Digital potentiometers (pots) offer advantages for audio volume (gain) control applications and can replace bulky mechanical pots, especially in handheld portable devices such as MP3 players
    Abstract: Digital potentiometers (pots) offer advantages for audio volume (gain) control applications and can replace bulky mechanical pots, especially in handheld portable devices such as MP3 players, PDAs, cell phones, mobile Internet devices, or stereo AM/FM radios. This document describes the types of digital pots available for audio control such as logarithmic taper pots (log pots). It examines several common designs using log taper pots and audio amplifiers, evaluates their advantages and disadvantages, and recommends circuit designs. 
    

    注册参加Maxim在TechOnline举办的在线研讨会</a> (English only)

    注册参加Maxim在TechOnline举办的在线研讨会
    (English only)
    A similar version of this article appeared in the January 7, 2002 issue of EE Times magazine.

    Introduction

    It is now common for portable multimedia equipment to include some sort of stereo audio playback circuitry, perhaps for MP3 or mobile Internet applications. Many specialized ICs are available for these circuits and many use a mechanical potentiometer (pot). This application note will demonstrate that widely available low-power components can be just as effective. The article demonstrates how to achieve a stereo volume control without a mechanical pot.

    Traditional Mechanical Pot Design

    Historically, audio volume controls used a special kind of potentiometer with a log (or sometimes audio) taper or law ( Figure 1). This approach derives from the roughly logarithmic response of the ear to changes in sound pressure levels.

    Figure 1. Logarithmic response of the potentiometer to changes in sound pressure levels.
    Figure 1. Logarithmic response of the potentiometer to changes in sound pressure levels.

    In general, the midpoint of the rotation usually gives around 20dB attenuation of the audio signal, with attenuation rapidly increasing from the midpoint counter-clock wise (CCW). There is finer control over the "louder" settings from the midpoint clock wise (CW).

    While this approach works well in practice, there are still several reasons not to use a mechanical pot in a small portable device. The space constraints and reliability issues of a mechanical pot are just two immediate issues. Today a common volume-control interface for modern devices uses up/down buttons in conjunction with some form of host processor. This design provides an inexpensive, useable solution without a bulky mechanical pot.

    Stereo (or ganged) rotary pots also have a mechanical tracking issue; mechanical tolerances mean that L-R tracking suffers as the volume is adjusted. Also, the desired transfer function should be considered. Is full attenuation desired? Or rather, can the application use a gain trim control offering perhaps 30dB of adjustment range but no fully off' position? Perhaps you should consider a digital pot?

    Design Issues with Digital Pots

    Over the past years digital pots have become available and their performance has evolved ( Figure 2). These digital devices use resistive ladders and FET switching under digital control to effectively replace mechanical pots in a number of areas. On the surface, using a pair of these ICs would seem a logical solution for stereo volume control, however, there are issues which must first be addressed.

    Figure 2. Functional block diagram of the MAX5160 digital pot.
    Figure 2. Functional block diagram of the MAX5160 digital pot.

    The most commonly available digital pots are effectively linear pots, i.e., their resistive increments are equally weighted. A reasonably constant dB-per-step law is desirable in audio volume control, so the design may have to emulate this log behavior in some way. Recall now that we are no longer constrained by the mechanical pot's audio taper.

    There is a follow-on issue. While the digital pot steps are usually designed to give equal-value resistive increments, a by-product of the process variation is that the total end-to-end resistance varies widely from part to part, as much as ±30% in some types. This resistance variation must be considered when designing a circuit that requires close matching between two channels using separate digital pots.

    Finally, the transitions should be as glitch free as possible, so a make-before-break wiper arrangement should be considered mandatory.

    Design Examples

    Some design examples follow. There are both gain-trim designs (where the control is applied over a set attenuation range, but not giving full attenuation), and more traditional full CW/off CCW volume controls. These circuit ideas assume a VCC of between 2.7V and 5V and a low-impedance V REF = V CC/2. The IN input signals are from a low-impedance voltage source.

    Example 1

    The circuit in Figure 3 would seem to give adequate results. Using two MAX5160Ls (assuming that their digital inputs are suitably controlled) around a MAX4252 op amp, the circuit should give evenly tracking gain or attenuation over a nominal ±6dB range. The circuit should work over a V CC range from 2.7V to 5V and have 32 useable gain settings. Even the power-on-reset ( POR) state of the MAX5160L gives approximately a unity gain setting.

    The drawback to this implementation is the ±25% overall resistance variation of the digital pot. This variation could lead to a wide gain tolerance, especially on the settings at the extremities of resistance, channel-to-channel as well as unit-to-unit. For example, assuming the 50kΩ resistors are ±1%, then the nominal, maximum +6dB setting could vary between limits of:
    Av1 = -(50.5kΩ + 62.5kΩ)/49.5kΩ = -2.283V/V or 7.16dB

    Av2 = -(49.5kΩ + 37.5kΩ)/50.5kΩ = -1.723V/V or 4.73dB
    Figure 3. ±6db stereo gain trim control, 32 gain settings (1 channel shown).
    Figure 3. ±6db stereo gain trim control, 32 gain settings (1 channel shown).

    This amount of left-right mismatch is easily audible. This circuit can be made to work better by selecting or trimming the support resistors (or selecting the digital pot!) to suit, but this is not feasible in mass production. A design approach must be found which minimizes or eliminates this gain error.

    Example 2

    The circuit in Figure 4 uses the MAX5160L digital pot in a divider chain. The MAX5160L uses 100kΩ and 50kΩ resistors to supply the MAX4252 with some positive feedback in addition to the usual negative feedback . The gain of this circuit can be shown as:
    AV = (1 - K N)/(K P - K N)
    Where K N is the negative feedback fraction and K P is the positive feedback fractions. For the example in Figure 4, K N = 100kΩ/(100kΩ + 50kΩ) or 2/3, and K P is variable.

    Figure 4. ±6dB stereo gain trim control, 17 gain settings in an improved design.
    Figure 4. ±6dB stereo gain trim control, 17 gain settings in an improved design.

    When the MAX5160L wiper is positioned at the V REF terminal, the gain of the circuit is -0.5V/V, as there is no positive feedback contribution. When the wiper is at midscale, K P = 0.5 and the gain is now -2V/V. Hence, by using those 17 positions between V REF and midscale, the gain can be varied over a ±6dB range. The 15 unused positions have been a trade-off for repeatability, because the gain value does not depend on the digital-pot resistance tolerance, as did the circuit of Figure 1. The gain tolerance is now only limited by the ±1% 100kΩ/50kΩ resistors and the INL/DNL error of the MAX5160L (±4.6%, max.).

    There is an interesting point to note. The limit for stability in this circuit is reached when K P ≥ 2/3, i.e., when the positive feedback fraction meets or exceeds the negative. The host processor controlling the MAX5160L should, therefore, prevent this situation from occurring.

    Example 3

    The circuit in Figure 5 uses digital pots as an obvious alternative to a traditional approach for volume control. All codes are valid, with settings ranging from 0dB to full attenuation. Table 1 shows the calculated attenuations based on the MAX5160L's 32 steps.

    Table 1. Calculated results of Figure 3 circuit
    Code SettingAttenuationCode SettingAttenuation
    00.0016-6.31
    1-0.2817-6.90
    2-0.5818-7.55
    3-0.8819-8.24
    4-1.2020-9.00
    5-1.5321-9.83
    6-1.8722-10.74
    7-2.2223-11.77
    8-2.5924-12.93
    9-2.9825-14.26
    10-3.3826-15.85
    11-3.8127-17.79
    12-4.2528-20.28
    13-4.7229-23.81
    14-5.2230-29.83
    15-5.7431Full attenuation

    Figure 5. Traditional volume control design (1 channel shown) has drawbacks.
    Figure 5. Traditional volume control design (1 channel shown) has drawbacks.

    Notice how the attenuation figures are spread. There is less than 6dB total variation over the first 15 codes and less than 1dB over the first four. This is not particularly useful. Interestingly, even when choosing a part with a far larger number of taps, you still only get 6dB variation over half of the codes.

    To address this problem one approach selects a subset of the codes available to achieve a reasonably constant dB/step figure. For example, using only those codes highlighted in Table 1 gives roughly 3dB/step up to code 29, allowing 11 settings. This can work well if the digital pot chosen has many tap positions (256 or higher). However, parts with that flexibility are generally more expensive. Given that the majority of the tap positions will not be used (unless, perhaps, when interpolating between volume settings), it would seem more efficient to try and utilize more of the existing taps with a different topology.

    Resistively loading the wiper of a linear pot to "bend" the characteristic is an old trick. The load resistor is usually about 1/20th the value of the linear pot resistance. There are two disadvantages of applying this method with a linear' digital pot: the input impedance of the pot is now dependant on gain setting (lowest at maximum volume); and again, the wide tolerance on end-to-end resistance means that L-R tracking suffers at any setting apart from the extremes. Figure 6 shows the idea.

    Figure 6. This configuration with a resistive load creates an equivalent fixed-resistor for clarity.
    Figure 6. This configuration with a resistive load creates an equivalent fixed-resistor for clarity.

    Example 4

    The circuit of Figure 7 yields a traditional volume-control characteristic, much like that of Figure 5. However, this design uses a little positive feedback to even out the step sizes to roughly 1.6dB/step over most of its useable range.

    An immediate disadvantage of this design is that the negative feedback fraction (K N) has to be 0.5 or higher for this approach to yield usable results (although 0.25 would be the limit of stability). In simple terms, we have already thrown away around half the available codes just so the circuit can operate. However, the remaining 17 codes are all used (no gaps as in the Figure 6 example), as indicated in Table 2 below. The third column lists the delta in step sizes, showing how consistent they are over the majority of the attenuation range. Figure 8 shows the linearising effect, with gain in dB on the Y-axis plotted against tap number on the X-axis. This data compares favorably with the circuit of Figure 6, where the highlighted values gave roughly 3dB steps and only 11 settings.

    Figure 7. This near-constant dB/step topology (1 channel shown) is an improved design.
    Figure 7. This near-constant dB/step topology (1 channel shown) is an improved design.

    One side effect of this topology with the values shown is that there will be a 6dB boost for the midscale value of the digital pot. This can often be accommodated in the gain structure of the full audio path, where some gain shifting is usually inevitable.

    Table 2. Calculated results of Figure 7 circuit
    Code SettingGain(Delta)Code SettingGain<(Delta)/td>
    166.88 24-5.601.61
    175.191.6825-7.321.71
    183.601.5926-9.171.86
    192.061.5427-11.252.07
    200.561.5028-13.652.40
    21-0.931.5029-16.592.94
    22-2.441.5130-20.533.94
    23-3.991.5531-26.956.42
       32Fully off

    Figure 8. Stereo, cascaded traditional volume control, more = better?
    Figure 8. Stereo, cascaded traditional volume control, more = better?

    Example 5

    The circuit of Figure 9 uses a total of four MAX5160L digital pots to produce a high-resolution, stereo volume control. The number of possible valid codes per channel is greatly increased, giving 32 x 32 or 1024 attenuation codes. Again, the end-to-end resistance tolerance does not have any first-order effect because of the buffering between the two digital pot stages. L-R tracking is only limited by the tap-to-tap matching accuracy. The wiper resistance has little loading effect, as each wiper sees a high-impedance op amp input.

    Figure 9. This design uses MAX1560L digital pots to produce high-resolution stereo volume control.
    Figure 9. This design uses MAX1560L digital pots to produce high-resolution stereo volume control.

    Of the 1024 codes, some give duplicate attenuation values. For example, the first pot is at -6dB and the second is fully up, thus giving -6dB overall. This is the same as first pot fully up and the second at -6dB., Moreover, if either pot is set to full attenuation, any setting on the other pot is irrelevant, all of which leaves something like 348 unique attenuation settings from 0 to -60dB (actually -59.66dB).

    To map the codes to an attenuation figure, some sort of simulation or spreadsheet approach would seem appropriate. Figure 10 shows the spread of attenuation obtained, including duplicate values.

    Figure 10. Spread of attenuation obtained from the design of Figure 9.
    Figure 10. Spread of attenuation obtained from the design of Figure 9.

    Figure 10 demonstrates that most of the codes give attenuation values between 0 and -40dB. The delta, or dB step size between each attenuation value, can be plotted in a manner similar to that in Table 2 ( Figure 11). This gives a visual indication of the granularity of the steps.

    Figure 11. Plot shows the delta in dB of the step size between each attenuation value for the codes generated by the Figure 9 circuit.
    Figure 11. Plot shows the delta in dB of the step size between each attenuation value for the codes generated by the Figure 9 circuit.

    The granularity of the steps appears very evenly distributed with differences in most of the steps well under 0.5dB, only reaching 1dB at -41.6dB, and with the penultimate 6dB step between -53.6 and -59.6. Repeated codes appear on the graph as zero delta figures. This yields the kind of control range and granularity required in the most exacting audio level controls.

    There are, however, limitations to this approach too. Obviously, this circuit has a reasonable control overhead, perhaps using lookup tables to retrieve values and using some kind of ranging algorithm to obtain smooth volume transitions. Unlike the circuit in Figure 4, however, there is no conditional stability situation so any combination of codes is fine. More seriously, variations in the tap-to-tap resistor matching between the first and second digital pots could mean that monotonicity is NOT guaranteed. Using a subset of the codes, hence coarser steps, would be one way of assuring monotonic steps, but this would come at the expense of fine steps.

    In theory, while the cascaded circuit of Figure 9 seems to give impressive results on initial investigation, the practical implementation of the circuit can be problematic.

    Summary

    The circuits of Figures 5 and 6 probably give the best compromise between price, complexity and performance for most situations. Controlled using a 3-wire interface, Maxim also offers the MAX5400/MAX5401 and MAX5402 devices. These digital pots offer 256 taps for those applications needing slightly higher resolution and have a 3-wire protocol available for control.
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  • 在Simulink中调整增益映射 Tune Gain Schedules in Simulink 文章目录调节增益调度的工作流程 Workflow for Tuning Gain Schedules1)选择一组设计点,充分覆盖你需要调优的操作范围2)获取一组在设计点处描述线性...

    通常,增益调度控制器是一种固定的单回路single-loop或者多回路multiloop控制结构,其中控制器增益随着操作条件变化。增益调度映射把描述当前运行状态current operating condition的调度变量scheduling variables转换成合适的控制器增益。在Simulink中,你可以使用查找表或者MATLAB函数来实现增益调度映射。

    参考在simulink中建立调度增益控制系统的模型 - 刘凯的博客 - CSDN博客

    如果已经有了Simulink Control Design™,可以使用systune来调节这些增益映射,最终使得完整的的非线性系统满足设计要求。调节增益调度映射等同于amounts to确定合适的查找表数据,或者是找到合适的MATLAB函数。对于systune,可以把增益调度参数化为具有可调节系数with tunable coefficients的调度变量的函数。

    调节增益调度的工作流程 Workflow for Tuning Gain Schedules

    1)选择一组设计点,充分覆盖你需要调优的操作范围

    设计点是一系列描述特定操作条件下的调度变量的值。这些设计点可以是规则的网络值regular grid of values,也可以是分散的集合scattered set。通常是从几个设计点开始,如果你调节出来的系统性能不在设计点之间,就增加更多的设计点。

    2)获取一组在设计点处描述线性动力学性能的线性模型

    获取这些线性模型数组的方法包括:

    • 在Simulink中,对网格中的每一个设计点(表示每一个运行条件)进行线性化。比如说,如果每个设计点代表一个稳态条件,你可以修剪trim模型plant的每一个设计点design point然后在最终的运行结果点resulting operating point处线性化。或者,如果调度变量是时间,可以在一系列的仿真快照simulation snapshots中线性化。
    • 在设计点对模型进行LPV建模Sample an LPV model of the plant at the design points.

    更多参考 Plant Models for Gain-Scheduled Controller Tuning

    3)创建一个slTuner接口来调优Simulink

    这样做的时候,将线性模型数组替换为模型substitute the array of linear models for the plant,以便slTuner接口包含一系列对应每个设计点的闭环可调节模型。

    更多参考Multiple Design Points in slTuner Interface

    4)把增益调度映射建模成参数增益曲面Model the gain schedules as parametric gain surfaces

    参数增益曲面parametric gain surfaces是一个具有可调节系数的基础函数展开式basis-function expansion,例如对于一个调度变量向量 σ \sigma σ而言,展开形式为:
    K ( σ ) = K 0 + K 1 F 1 ( n ( σ ) ) + … + K M F M ( n ( σ ) ) K(\sigma)=K_{0}+K_{1} F_{1}(n(\sigma))+\ldots+K_{M} F_{M}(n(\sigma)) K(σ)=K0+K1F1(n(σ))++KMFM(n(σ))
    n ( σ ) n(\sigma) n(σ)是一个归一化normalization 函数,在systune调优中,可以使用tunableSurface来表示参数增益曲面parametric gain surface K ( σ ) K(\sigma) K(σ)。在为调优创建的slTuner接口中,使用setBlockParam将得到的增益表面gain surface和表示增益调度的块block联系起来。systune对所有的设计点的系数 K 0 … , K M K_{0^{}} \ldots, K_{M} K0,KM进行调优。

    更多参考 Parameterize Gain Schedules

    5)使用TuningGoal对象来确定你的调优目标

    你可以指定specify适用于apply to所有设计点或者一个设计点子集的调优目标。你还可以指定随设计点变化vary的调优目标tuning goal。比如,你可能想要定义一个最小增益裕度minimum gain margin,这个最小裕度会随着某个特定调度变量particular scheduling variable大小magnitude的增加而变得越来越严格stringent 。

    更多关于指定随着设计点变化的调优目标,参考 Change Requirements with Operating Condition

    更多关于整体调优目标,参考 Tuning Goals

    6)使用systune来调优控制系统

    systune调节一系列参数 K 0 … , K M K_{0^{}} \ldots, K_{M} K0,KM(参数集),来同时针对against 模型中的所有设计网格design grid(多模型调优multimodel tuning) 。

    7)验证调优结果Validate the tuning results

    你可以检查调谐增益表面,并验证在每个设计点处线性系统的性能。

    但是,局部线性性能并不能保证在非线性系统中的全局性能。因此,使用调谐增益调度tuned gain schedules来验证仿真simulation-based validation效果是非常重要的。

    更多参考Validate Gain-Scheduled Control Systems

    参考Tune Gain Schedules in Simulink - MATLAB & Simulink - MathWorks 中国

    展开全文
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