发送到同一频道的连续MIDI消息被篡改

我正在编写一个简单的C++命令行实用程序,通过罗兰UM One Mk 2 USB接口将MIDI消息从我的Mac(MacOS 10.12)发送到贝林格Powerplay P16-m音频混音器。我正在使用 rtmidi realtime MIDI API 。

当我向同一频道发送两条连续的MIDI消息时,这两条消息似乎被混音器弄乱了。当我向备用频道发送两条连续消息时,效果很好。

例如,为了将通道1级别设置为midi 0(-51dB),将通道1 pan设置为midi 64(居中),我知道我应该发送以下两条消息: 0xB0 0x07 0x0 和 0xB0 0x0A 0x40 . 当我一个接一个地发送这些消息时,混音器上的LED意外地指示通道1的级别大约为64,并且平移没有改变——就像我发送了一条消息一样 0xB0 0x07 0x40 . 相反,如果我在这两条消息中穿插另一个通道的消息,或者睡眠时间长得离谱(任何超过900毫秒的时间都可以),LED指示预期的设置:水平为零,平移居中。

我做错了什么?为什么我不能向同一频道发送两条连续的消息?我是不是发信息太快了?这是一个 rtmidi 问题这是搅拌机的问题吗?

这里有一个最小但完整的工作示例来演示这个问题。(我使用XCode对CoreMIDI、CoreAudio和CoreFoundation框架进行编译。)

#include <iostream>
#include <vector>
#include <unistd.h> // (for usleep)
#include "RtMidi.h"

// define some midi messages
static std::vector<unsigned char> ch1vol {0xB0 , 0x07 , 0x0}; //  set ch 1 volume to midi 0 (-51dB)
static std::vector<unsigned char> ch1pan {0xB0 , 0x0A , 0x40}; // set ch 1 pan to 64
static std::vector<unsigned char> ch2vol {0xB1 , 0x07 , 0x0}; // set ch 2 volume to midi 0 (-51dB)
static std::vector<unsigned char> ch2pan {0xB1 , 0x0A , 0x40}; // set ch 2 pan to 64

#define SLEEPMSEC( milliseconds ) usleep( (unsigned long) (milliseconds * 1000.0) )

int main(int argc, const char * argv[]) {

    RtMidiOut * midiOut = new RtMidiOut(); // create an RtMidiOut

    // are there any midi ports available?
    if (!midiOut->getPortCount()) {
        std::cout << "*** No midi ports found. Goodbye." << std::endl;
        exit(1);
    }

    // open the desired midi device
    std::string portName = midiOut->getPortName(0);
    if (portName != "Powerplay 16") {
        std::cout << "*** Can't find requested midi device. Goodbye." << std::endl;
        exit(1);
    }
    midiOut->openPort(0); // open the midi device to receive output

    switch(argc) {
        case 2:
            // This works as expected
            // Result: channels 1 and 2 volumes are set to 0; the panning in both channels is centered)
            midiOut->sendMessage( &ch1vol ); // set ch 1 volume to 0
            midiOut->sendMessage( &ch2vol ); // set ch 2 volume to 0
            midiOut->sendMessage( &ch1pan ); // set ch 1 pan to center
            midiOut->sendMessage( &ch2pan ); // set ch 2 pan to center
            break;
        case 3:
            // This does NOT work as expected
            // Result: channels 1 and 2 volumes are set to 64; the panning in both channels is  unchanged
            midiOut->sendMessage( &ch1vol ); // set ch 1 volume to 0
            midiOut->sendMessage( &ch1pan ); // set ch 1 pan to center
            midiOut->sendMessage( &ch2vol ); // set ch 2 volume to 0
            midiOut->sendMessage( &ch2pan ); // set ch 2 pan to center
            break;
        case 4:
            // Introduce a sleep in between same-channel calls.
            // This DOES work as expected (but with an unacceptable delay)
            midiOut->sendMessage( &ch1vol ); // set ch 1 volume to 0
            SLEEPMSEC(900);
            midiOut->sendMessage( &ch1pan ); // set ch 1 pan to center
            midiOut->sendMessage( &ch2vol ); // set ch 2 volume to 0
            SLEEPMSEC(900);
            midiOut->sendMessage( &ch2pan ); // set ch 2 pan to center
            break;
        default:
            std::cout << "Usage: testmidi ARG [ARG [ARG]]" << std::endl;
            std::cout << "Perform a midi test according to the number of arguments." << std::endl;
            std::cout << "Be sure to reset the device manually after each run." << std::endl;
            break;
    }
}