diff --git a/src/stream.cpp b/src/stream.cpp
--- a/src/stream.cpp
+++ b/src/stream.cpp
@@ -142,39 +142,72 @@ void Stream::setNumChannels(unsigned nc,
     Sink::setNumChannels(nc, x);
 }
 
-void Stream::feedIn(const SamplePack& data)
+const SamplePack* Stream::applyGainOffset(const SamplePack& pack) const
 {
-    Q_ASSERT(data.numChannels() == numChannels() &&
-             data.hasX() == hasX());
+    SamplePack* mPack = nullptr;
+    unsigned ns = pack.numSamples();
+
+    for (unsigned ci = 0; ci < numChannels(); ci++)
+    {
+        bool gainEn = channels[ci]->info()->gainEn(ci);
+        bool offsetEn = channels[ci]->info()->offsetEn(ci);
+        double* mdata;
+        if (gainEn || offsetEn)
+        {
+            if (mPack == nullptr)
+                mPack = new SamplePack(pack);
+
+            mdata = mPack->data(ci);
+
+            double gain = channels[ci]->info()->gain(ci);
+            double offset = channels[ci]->info()->offset(ci);
+
+            if (gainEn)
+            {
+                for (unsigned i = 0; i < ns; i++)
+                {
+                    mdata[i] *= gain;
+                }
+            }
+            if (offsetEn)
+            {
+                for (unsigned i = 0; i < ns; i++)
+                {
+                    mdata[i] += offset;
+                }
+            }
+        }
+    }
+
+    return mPack;
+}
+
+void Stream::feedIn(const SamplePack& pack)
+{
+    Q_ASSERT(pack.numChannels() == numChannels() &&
+             pack.hasX() == hasX());
 
     if (_paused) return;
 
-    unsigned ns = data.numSamples();
+    unsigned ns = pack.numSamples();
     if (_hasx)
     {
-        static_cast<RingBuffer*>(xData)->addSamples(data.xData(), ns);
+        static_cast<RingBuffer*>(xData)->addSamples(pack.xData(), ns);
     }
+
+    // modified pack that gain and offset is applied to
+    const SamplePack* mPack = applyGainOffset(pack);
+
     for (unsigned ci = 0; ci < numChannels(); ci++)
     {
-        // TODO: check for gainEn and offsetEn
-        // apply gain and offset
-        auto rdata = data.data(ci);
-        auto mdata = new double[sizeof(double) * ns];
-        // TODO: add gain&offset access methods to `StreamChannel`
-        double gain = channels[ci]->info()->gain(ci);
-        double offset = channels[ci]->info()->offset(ci);
-        for (int i = 0; i < ns; i++)
-        {
-            mdata[i] = rdata[i] * gain + offset;
-        }
-
-        static_cast<RingBuffer*>(channels[ci]->yData())->addSamples(mdata, ns);
-        delete[] mdata;
+        auto buf = static_cast<RingBuffer*>(channels[ci]->yData());
+        double* data = (mPack == nullptr) ? pack.data(ci) : mPack->data(ci);
+        buf->addSamples(data, ns);
     }
 
-    // TODO: emit modified (gain&offset) data
-    Sink::feedIn(data);
+    Sink::feedIn((mPack == nullptr) ? pack : *mPack);
 
+    if (mPack != nullptr) delete mPack;
     emit dataAdded();
 }
 
diff --git a/src/stream.h b/src/stream.h
--- a/src/stream.h
+++ b/src/stream.h
@@ -69,7 +69,7 @@ public:
 protected:
     // implementations for `Sink`
     virtual void setNumChannels(unsigned nc, bool x);
-    virtual void feedIn(const SamplePack& data);
+    virtual void feedIn(const SamplePack& pack);
 
 signals:
     void numChannelsChanged(unsigned value);
@@ -98,6 +98,19 @@ private:
     QList<StreamChannel*> channels;
 
     ChannelInfoModel _infoModel;
+
+    /**
+     * Applies gain and offset to given pack.
+     *
+     * If gain or offset isn't enabled this function returns `nullptr`. If gain
+     * or offset is enabled for at least 1 channel input pack is copied and
+     * modified. Result is returned. Caller is responsible for deleting
+     * returned `SamplePack`.
+     *
+     * @param pack input data
+     * @return `nullptr` if no gain or offset is enabled otherwise modified data
+     */
+    const SamplePack* applyGainOffset(const SamplePack& pack) const;
 };