标题：[原创]关于MAXXBASS和差频的疑问
坛子里有兄弟说MAXXBASS是运用差频来扩展低频下限的。我昨晚突然想到一个问题：双声道录音经音箱重放后为什么没有产生差频？用一只音箱听和用两只音箱听并不能感觉到下潜有扩展（如果是很小的音箱可能例外，因小音箱低音量太小容易被掩盖，所以加多一只音箱可能会好一点）。既然双声道录音并用两只音箱重放没有产生差频，为什么MAXXBASS却说它能利用差频扩展低音下限频率？要知道，为不改变音乐原来的音色，谐波频率成分比例是不应该变的，如果变了的话音色会不一样。所以MAXXBASS加进去的谐波应该跟音乐原来的谐波比例一样。
PHENOMENON OF THE MISSING FUNDAMENTAL
The Phenomenon of the Missing Fundamental was discovered initially by pipe organ builders during the 1700s. The large cathedrals during the Middle Ages had huge pipe organs that with pipes up to forty feel long to generate the really low frequencies that helped draw crowds of people to these church services to feel the bass as well as hear the spiritual message Some composers of pipe organ music found that they could “trick: the listener into hearing low bass tones that weren’t really there if the played a certain combination of notes that were higher than the low tone or “fundamental” that they wanted to be heard. For example, if they wanted the listener to hear a low C then they could play a C an octave higher and a G above that, and the low C would magically appear in the listener’ head.
The Phenomenon of the Missing Fundamental has also been studied and proven by many distinguished audio scientists such as Helmholtz, who discovered how vented port and vents operate. The perceived pitch of a combination of tones spaced equally in frequency is usually not that of the mean frequency, but rather that of the constant difference frequency. The constant difference frequency is the missing fundamental.
MAXXBASS
Meir Shashoua, the CTO of Waves, developed a theory on how the Phenomenon of the Missing Fundamental could be applied to loudspeaker reproduction limitations. Waves, the leader in audio signal processing ‘plug-ins’ tools for the professional audio market, leveraged its world leadership psychoacoustics to improve and sharpen this psychoacoustic effect. This technology, called MaxxBass was patented (U.S. Patent #5,930,373). MaxxBass has also been patented in
Waves MaxxBass and second generation Renaissance Bass plug-in utilize this technology and have become a standard tool over the past few years in creation of much of the world’s most popular music. These software tools are used to improve bass punch on bass limited systems. This is important on popular music may be played on everything from a dance floors with subwoofer arrays to small portable systems with severely limited bass capability. An example of the music mixed with this MaxxBass technology is “Lady Marmalade” by Christina Aguilera
The MaxxBass is even more effective when implemented directly in consumer audio reproduction systems, since the MaxxBass can be ‘tuned’ to the specific loudspeaker parameters improving performance on any audio bass content. This is now possible due to a cost-effective MX3000AS ASIC (Application Specific Integrated Circuit) as well as DSP software licensing from Waves.
Another significant advantage of implementing MaxxBass in consumer audio equipment is that this solution, unlike the professional audio editing tools, includes a high pass filter (HPF) removing the original bass frequencies that can not be reproduced by the loudspeaker. These frequencies are no longer needed since MaxxBass reproduces these through psychoacoustics. The HPF eliminates damaging speaker excursion, unnecessary power consumption and undesirable intermodulation distortion in the loudspeaker.
Boosting the low-frequency performance of a speaker by 1-1.5 octaves normally requires both increased headroom in the amplifier and increased excursion in the driver, plus extra Bl to maintain control at high excursion, all of which involve substantially more cost than implementing MaxxBass. MaxxBass is a powerful and cost-effective technology to audio system designers to improve bass response. It has widespread applications across audio applications including automotive, home audio, television, portable and personal audio.
Eagle
要知道人耳是很敏感的，现在还不存在绝对“不改变音乐原来的音色”的系统。既然都是失真的，何不利用失真来增加一点“快感”？
我估计这是MAXXBASS设计的初衷。
MAXBASS是我认为是利用了人耳的反应迟钝性,利用这个时间差,给人一种虚拟的声像!
实际效果没有我们他们说的那么好!
ALTEC 公司的多媒体音箱有用这技术,效果没有什么明显的
在下的老本行是研究听觉感知。此技术实际上是利用了人耳的一种听觉感知原理：当人在听一个有基波和偶次谐波的声波时，会误以为是该偶次谐波的基波在发音（这说明人耳是一个非线性系统，听到的是基波和偶次谐波的差频）。而且人耳天生就喜欢听偶次谐波，（不信各位试试看：放一个正弦波，再放一个同频的三角波，看你喜欢听那一种，我敢100%地肯定你一定喜欢由偶次谐波组成的三角波，哪怕你完全不懂音乐，这也正是电子管功放保留至今的原因）由于偶次谐波比基波频率高，自然发音效率也高，于是可以减小喇叭的口径，用发偶次谐波来欺骗耳朵。其实，在下早在十多年前就突发灵感，实施了该解决方案，并寄托了极大希望，结果可以告诉大家，的确明显增强了低音，但是实话实说，也改变了感觉到的音质，与原来的音质有明显的差别！而且增强的低音听感上远不像原来的低音。结果迎头给我浇了一盆凉水，在下属于追求完美的的发烧友，自然从此不再对此技术感冒。当然，在今天看来，在IT的低档多媒体音响中还是大有用武之地的。按在下的解决方案，远比MAXBASS要简单，价廉得多，成本仅只增加几元钱。
各位，待在下一一道来：
在下的老本行是研究听觉感知。此技术实际上是利用了人耳的一种听觉感知原理：当人在听一个有基波和偶次谐波的声波时，会误以为是该偶次谐波的基波在发音（这说明人耳是一个非线性系统，听到的是基波和偶次谐波的差频）。而且人耳天生就喜欢听偶次谐波，（不信各位试试看：放一个正弦波，再放一个同频的三角波，看你喜欢听那一种，我敢100%地肯定你一定喜欢由偶次谐波组成的三角波，哪怕你完全不懂音乐，这也正是电子管功放保留至今的原因）由于偶次谐波比基波频率高，自然发音效率也高，于是可以减小喇叭的口径，用发偶次谐波来欺骗耳朵。其实，在下早在十多年前就突发灵感，实施了该解决方案，并寄托了极大希望，结果可以告诉大家，的确明显增强了低音，但是实话实说，也改变了感觉到的音质，与原来的音质有明显的差别！而且增强的低音听感上远不像原来的低音。结果迎头给我浇了一盆凉水，在下属于追求完美的的发烧友，自然从此不再对此技术感冒。当然，在今天看来，在IT的低档多媒体音响中还是大有用武之地的。按在下的解决方案，远比MAXBASS要简单，价廉得多，成本仅只增加几元钱。
来了一个研究听感的大哥！佩服！
不过，“信各位试试看：放一个正弦波，再放一个同频的三角波，看你喜欢听那一种，我敢100%地肯定你一定喜欢由偶次谐波组成的三角波，哪怕你完全不懂音乐”如果这样做，我还是喜欢停正弦波而不搞那个刺耳的三角波。
另外，看看三角波的傅立叶展开吧，哪会是偶次谐波组成？
不知你的成本只增加几块钱是怎么算出来的，能解释一下吗？
列位：低音增强技术实际上是与HiFi背道而驰的，不是减少失真，而恰恰相反的是要增加偶次谐波失真。因此，在信号处理电路中要加入非线性处理数学模型，方法有二：一是用模拟电路实现；二是在DSP中用数字信号处理实现，国外的解决方案是用第二种解决方案，能够精确地实现所需的非线性数学模型，但成本自然居高不下。实际上，现在的微型音响音质不过如此，用高精度的DSP解决方案实有杀鸡用牛刀之嫌。实际上直接用模拟电路即可实现，效果也挺不错，本人正是用的模拟电路解决方案，已开发出产品原型，成本仅为国外方案的1/10或更低。
zhigang324兄，可能有些错误
锯齿波包含了所有次数的谐波，三角波只包含很少的谐波，以奇数次谐波居多。
正弦波：
此主题相关图片如下：
三角波：此主题相关图片如下：
锯齿波：此主题相关图片如下：
已经改变声音的音色了，对高保真来说可能不行
ZHIG324兄的研究有些悬,孰奇孰偶呀?
多数电子管功放是推挽式的,主要失真恰是奇次谐波.
任何地方,信号的"偶次谐波比基波频率高"都成立.
您的"的模拟电路解决方案"看来就是"偏压二极管"之类的DD吧.
说什么偶次就悦耳奇次就刺耳，那是想当然的说法吧。
声音感受是跟谐波有关，但绝非是奇次偶次那么简单。