====== Avoid new/delete, prefer references to pointers, use member variables for sub-Components ======
The JUCE library includes a nice collection of //managed pointer// template classes, such as //juce::ScopedPointer//, which can and should be used to avoid most uses of the ''delete'' keyword. Note that managed pointers are still assigned using ''new''.

I checked my code carefully, and was unable to find any uses of ''delete'', and found none. I did find a number of uses of ''new'', however, which fell into two categories:
  - In my //VanillaJuceAudioProcessor// class, I used ''new'' to create object-instances where there was effectively no choice; the JUCE library itself required it. I also used ''new'' when when creating //juce::XmlElement// objects, following the example of the JUCE static function //juce::AudioProcessor::getXmlFromBinary()//, which returns a non-managed pointer.
  - In all of my GUI-related classes, I used ''new'' to create various //juce::Component// objects, assigning the result to //juce::ScopedPointer// member variables of the //Gui...// class. I used the Projucer to generate this code, and that's what it produced, so I assumed this was the recommended approach. I have since learned, through discussion on the JUCE Forum, that this is definitely not the case.

Regarding the first category, I can only assume that Jules's admonition to "ditch all your new/delete..." was something of a generic complaint. Regarding the GUI-related classes, I now understand that the Projucer's lavish use of //ScopedPointer// is not at all recommended, and that child //Component// objects should ideally be declared as member variables.

===== Cleaning up the GUI classes =====
JUCE Forum user //Holy_City// provided the following code-example showing a variety of tricks for reducing the size of constructor functions for //juce::Component//-derived classes:
<code cpp>
lass EnvelopeComponent : public Component
{
public:
    EnvelopeComponent() /* user the initializer list */
    :    attack (Slider::Rotary, Slider::noTextBox), //very helpful constructor for Sliders
         decay  (Slider::Rotary, Slider::noTextBox),
         sustain (Slider::Rotary, Slider::noTextBox),
         release (Slider::Rotary, Slider::noTextBox)
    {
        auto initSlider = [this] (Slider& s)  // lambda expression declaration
        {
            addAndMakeVisible (s):
            s.setRange (1.0, 500.0);
            s.setValue (25.0);
        };

         initSlider (attack);
         initSlider (decay);
         initSlider (release);
         
         addAndMakeVisible (sustain);
         sustain.setRange (0.0, 1.0);
         sustain.setValue (0.707);
    }
    //.... yada yada yada 
private:
    Slider attack, sustain, decay, release; /* don't need to put them on different lines */
};
</code>

Following //Holy_City//'s example I was able to reduce the //GuiEgTab// class from this:
<code cpp>
class GuiEgTab  : public Component,
                  public SliderListener
{
public:
    GuiEgTab (SynthSound* pSynthSound);
    ~GuiEgTab();

    void paint (Graphics& g) override;
    void resized() override;
    void sliderValueChanged (Slider* sliderThatWasMoved) override;

    void notify();

private:
    SynthSound* pSound;

    ScopedPointer<Label> attackLabel;
    ScopedPointer<Slider> attackSlider;
    ScopedPointer<Label> decayLabel;
    ScopedPointer<Slider> decaySlider;
    ScopedPointer<Label> sustainLabel;
    ScopedPointer<Slider> sustainSlider;
    ScopedPointer<Label> releaseLabel;
    ScopedPointer<Slider> releaseSlider;

    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (GuiEgTab)
};

GuiEgTab::GuiEgTab (SynthSound* pSynthSound)
    : pSound(pSynthSound)
{
    addAndMakeVisible (attackLabel = new Label ("attack label",
                                                TRANS("Attack Time (sec)")));
    attackLabel->setFont (Font (15.00f, Font::plain).withTypefaceStyle ("Regular"));
    attackLabel->setJustificationType (Justification::centredRight);
    attackLabel->setEditable (false, false, false);
    attackLabel->setColour (TextEditor::textColourId, Colours::black);
    attackLabel->setColour (TextEditor::backgroundColourId, Colour (0x00000000));

    addAndMakeVisible (attackSlider = new Slider ("attack time slider"));
    attackSlider->setRange (0, 10, 0);
    attackSlider->setSliderStyle (Slider::LinearHorizontal);
    attackSlider->setTextBoxStyle (Slider::TextBoxRight, false, 80, 20);
    attackSlider->addListener (this);

    addAndMakeVisible (decayLabel = new Label ("decay time label",
                                               TRANS("Decay Time (sec)")));
    decayLabel->setFont (Font (15.00f, Font::plain).withTypefaceStyle ("Regular"));
    decayLabel->setJustificationType (Justification::centredRight);
    decayLabel->setEditable (false, false, false);
    decayLabel->setColour (TextEditor::textColourId, Colours::black);
    decayLabel->setColour (TextEditor::backgroundColourId, Colour (0x00000000));

    addAndMakeVisible (decaySlider = new Slider ("decay time slider"));
    decaySlider->setRange (0, 10, 0);
    decaySlider->setSliderStyle (Slider::LinearHorizontal);
    decaySlider->setTextBoxStyle (Slider::TextBoxRight, false, 80, 20);
    decaySlider->addListener (this);

    addAndMakeVisible (sustainLabel = new Label ("sustain level label",
                                                 TRANS("Sustain Level (%)")));
    sustainLabel->setFont (Font (15.00f, Font::plain).withTypefaceStyle ("Regular"));
    sustainLabel->setJustificationType (Justification::centredRight);
    sustainLabel->setEditable (false, false, false);
    sustainLabel->setColour (TextEditor::textColourId, Colours::black);
    sustainLabel->setColour (TextEditor::backgroundColourId, Colour (0x00000000));

    addAndMakeVisible (sustainSlider = new Slider ("sustain level slider"));
    sustainSlider->setRange (0, 100, 1);
    sustainSlider->setSliderStyle (Slider::LinearHorizontal);
    sustainSlider->setTextBoxStyle (Slider::TextBoxRight, false, 80, 20);
    sustainSlider->addListener (this);

    addAndMakeVisible (releaseLabel = new Label ("release time label",
                                              TRANS("Release Time (sec)")));
    releaseLabel->setFont (Font (15.00f, Font::plain).withTypefaceStyle ("Regular"));
    releaseLabel->setJustificationType (Justification::centredRight);
    releaseLabel->setEditable (false, false, false);
    releaseLabel->setColour (TextEditor::textColourId, Colours::black);
    releaseLabel->setColour (TextEditor::backgroundColourId, Colour (0x00000000));

    addAndMakeVisible (releaseSlider = new Slider ("release time slider"));
    releaseSlider->setRange (0, 10, 0);
    releaseSlider->setSliderStyle (Slider::LinearHorizontal);
    releaseSlider->setTextBoxStyle (Slider::TextBoxRight, false, 80, 20);
    releaseSlider->addListener (this);

    notify();
}

GuiEgTab::~GuiEgTab()
{
}

//==============================================================================
void GuiEgTab::paint (Graphics& g)
{
    g.fillAll (Colour (0xff323e44));
}

void GuiEgTab::resized()
{
    const int labelLeft = 16;
    const int controlLeft = 144;
    const int labelWidth = 120;
    const int sliderWidth = 420;
    const int controlHeight = 24;
    const int gapHeight = 8;

    int top = 20;
    attackLabel->setBounds (labelLeft, top, labelWidth, controlHeight);
    attackSlider->setBounds (controlLeft, top, sliderWidth, controlHeight);
    top += controlHeight + gapHeight;
    decayLabel->setBounds (labelLeft, top, labelWidth, controlHeight);
    decaySlider->setBounds (controlLeft, top, sliderWidth, controlHeight);
    top += controlHeight + gapHeight;
    sustainLabel->setBounds (labelLeft, top, labelWidth, controlHeight);
    sustainSlider->setBounds (controlLeft, top, sliderWidth, controlHeight);
    top += controlHeight + gapHeight;
    releaseLabel->setBounds (labelLeft, top, labelWidth, controlHeight);
    releaseSlider->setBounds (controlLeft, top, sliderWidth, controlHeight);
}

void GuiEgTab::sliderValueChanged (Slider* sliderThatWasMoved)
{
    double value = sliderThatWasMoved->getValue();
    SynthParameters* pParams = pSound->pParams;
    if (sliderThatWasMoved == attackSlider)
    {
        pParams->ampEgAttackTimeSeconds = value;
    }
    else if (sliderThatWasMoved == decaySlider)
    {
        pParams->ampEgDecayTimeSeconds = value;
    }
    else if (sliderThatWasMoved == sustainSlider)
    {
        pParams->ampEgSustainLevel = 0.01 * value;
    }
    else if (sliderThatWasMoved == releaseSlider)
    {
        pParams->ampEgReleaseTimeSeconds = value;
    }
    pSound->parameterChanged();
}

void GuiEgTab::notify()
{
    SynthParameters* pParams = pSound->pParams;
    attackSlider->setValue(pParams->ampEgAttackTimeSeconds);
    decaySlider->setValue(pParams->ampEgDecayTimeSeconds);
    sustainSlider->setValue(100.0 * pParams->ampEgSustainLevel);
    releaseSlider->setValue(pParams->ampEgReleaseTimeSeconds);
}
</code>
to this:
<code cpp>
class GuiEgTab  : public Component,
                  public SliderListener
{
public:
    GuiEgTab (SynthSound* pSynthSound);

    void paint (Graphics& g) override;
    void resized() override;
    void sliderValueChanged (Slider* sliderThatWasMoved) override;

    void notify();

private:
    SynthSound* pSound;

    Label attackLabel, decayLabel, sustainLabel, releaseLabel;
    Slider attackSlider, decaySlider, sustainSlider, releaseSlider;

    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (GuiEgTab)
};

GuiEgTab::GuiEgTab (SynthSound* pSynthSound)
    : pSound(pSynthSound)
    , attackLabel("attack", TRANS("Attack Time (sec)"))
    , decayLabel("decay", TRANS("Decay Time (sec)"))
    , sustainLabel("sustain", TRANS("Sustain Level (%)"))
    , releaseLabel("release", TRANS("Release Time (sec)"))
{
    auto initLabel = [this](Label& label)
    {
        addAndMakeVisible(label);
        label.setFont (Font (15.00f, Font::plain).withTypefaceStyle ("Regular"));
        label.setJustificationType (Justification::centredRight);
        label.setEditable (false, false, false);
        label.setColour (TextEditor::textColourId, Colours::black);
        label.setColour (TextEditor::backgroundColourId, Colour (0x00000000));
    };

    initLabel(attackLabel);
    initLabel(decayLabel);
    initLabel(sustainLabel);
    initLabel(releaseLabel);

    auto initSlider = [this](Slider& slider)
    {
        addAndMakeVisible(slider);
        slider.setSliderStyle (Slider::LinearHorizontal);
        slider.setTextBoxStyle (Slider::TextBoxRight, false, 80, 20);
        slider.addListener (this);
    };

    initSlider(attackSlider); attackSlider.setRange (0, 10, 0);
    initSlider(decaySlider); decaySlider.setRange (0, 10, 0);
    initSlider(sustainSlider); sustainSlider.setRange (0, 100, 1);
    initSlider(releaseSlider); releaseSlider.setRange (0, 10, 0);

    notify();
}

void GuiEgTab::paint (Graphics& g)
{
    g.fillAll (Colour (0xff323e44));
}

void GuiEgTab::resized()
{
    const int labelLeft = 16;
    const int controlLeft = 144;
    const int labelWidth = 120;
    const int sliderWidth = 420;
    const int controlHeight = 24;
    const int gapHeight = 8;

    int top = 20;
    attackLabel.setBounds (labelLeft, top, labelWidth, controlHeight);
    attackSlider.setBounds (controlLeft, top, sliderWidth, controlHeight);
    top += controlHeight + gapHeight;
    decayLabel.setBounds (labelLeft, top, labelWidth, controlHeight);
    decaySlider.setBounds (controlLeft, top, sliderWidth, controlHeight);
    top += controlHeight + gapHeight;
    sustainLabel.setBounds (labelLeft, top, labelWidth, controlHeight);
    sustainSlider.setBounds (controlLeft, top, sliderWidth, controlHeight);
    top += controlHeight + gapHeight;
    releaseLabel.setBounds (labelLeft, top, labelWidth, controlHeight);
    releaseSlider.setBounds (controlLeft, top, sliderWidth, controlHeight);
}

void GuiEgTab::sliderValueChanged (Slider* sliderThatWasMoved)
{
    double value = sliderThatWasMoved->getValue();
    SynthParameters* pParams = pSound->pParams;
    if (sliderThatWasMoved == &attackSlider) pParams->ampEgAttackTimeSeconds = value;
    else if (sliderThatWasMoved == &decaySlider) pParams->ampEgDecayTimeSeconds = value;
    else if (sliderThatWasMoved == &sustainSlider) pParams->ampEgSustainLevel = 0.01 * value;
    else if (sliderThatWasMoved == &releaseSlider) pParams->ampEgReleaseTimeSeconds = value;
    pSound->parameterChanged();
}

void GuiEgTab::notify()
{
    SynthParameters* pParams = pSound->pParams;
    attackSlider.setValue(pParams->ampEgAttackTimeSeconds);
    decaySlider.setValue(pParams->ampEgDecayTimeSeconds);
    sustainSlider.setValue(100.0 * pParams->ampEgSustainLevel);
    releaseSlider.setValue(pParams->ampEgReleaseTimeSeconds);
}
</code>