Client

A media and entertainment company aimed to build a real-time voice changer app for Android. They wanted:

• Live voice effects

• Fast audio processing

• Pitch shifting and tempo modification

• High-quality MP3 recording

• Minimal latency

• Compatibility with different Android devices

• Smooth UI and instant playback

Their existing prototype used basic AudioTrack/AudioRecord pipelines with Java processing, which resulted in:

• High latency

• Poor quality effects

• CPU overload on mid-range devices

• Inconsistent behavior across Android versions

They needed a native, high-performance audio processing engine.

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Project Overview

We engineered a real-time voice processing engine using:

• FFmpeg for decoding, filtering, and mixing

• libmp3lame for high-quality MP3 encoding

• SoundTouch for real-time pitch & tempo manipulation

• Native C/C++ code (JNI) for low-latency audio pipeline

• OpenSL ES / AAudio for fast audio I/O

The final app provides instant voice effects during recording or playback.

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Key Challenges

1. Achieving Real-Time Processing

Applying pitch, tempo, and filter effects without delay required native audio processing pipelines.

2. Audio Latency Issues

Typical Java-based audio APIs created latency that made live voice changing unusable.

3. Cross-Device Compatibility

Different Android devices use:

• Different sample rates

• Different buffers

• Different audio hardware paths

Ensuring consistent performance was crucial.

4. High-Quality Encoding

The client required high-quality MP3 export, not raw PCM.

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Our Solution

1. Native Audio Pipeline Using C++ & JNI

We built:

• Native audio engine

• Real-time audio buffer queues

• Separate threads for input, processing, output

This ensured minimal latency and smoother playback.

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2. SoundTouch for Real-Time Pitch & Tempo Manipulation

We integrated SoundTouch with custom optimizations:

• Pitch shifting

• Tempo changes

• Voice deepening/high effects

• Robot, chipmunk, monster, echo effects

Optimizations included:

• SIMD acceleration where available

• Reduced buffer copies

• Custom tuning for responsiveness

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3. FFmpeg for Audio Filters and Pre/Post Processing

FFmpeg was compiled with:

• libswresample

• audio filters

• libavcodec / libavutil

Used for:

• Equalizer effects

• Reverb, chorus, echo

• Noise reduction

• Format conversion

• Mixing background audio

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4. libmp3lame for High-Quality MP3 Export

Many voice changer apps export low-quality audio.
We enabled:

• 128 kbps / 192 kbps MP3

• CBR or VBR modes

• Efficient real-time streaming into encoder

This provided studio-grade output quality.

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5. Real-Time Input/Output via OpenSL ES or AAudio

Depending on device:

• OpenSL ES for older versions

• AAudio for Android 8+

Benefits:

• Low-latency recording

• Smooth playback

• Less jitter

• Stable buffer flow

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6. Custom Audio Mixer & Effects Layer

We built a flexible effects engine that lets users:

• Chain multiple effects

• Adjust effect intensity with sliders

• Preview changes in real time

• Apply filters to pre-recorded clips

Effects included:

• Pitch shift

• Tempo change

• Echo

• Reverb

• Distortion

• Radio effect

• Background music mixing

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7. Cross-Device Compatibility Handling

We added:

• Automatic sample rate detection (44.1kHz / 48kHz)

• Dynamic buffer negotiation

• Fallback paths for low-end devices

• Graceful degradation when hardware is limited

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Architecture Diagram (Text Version)

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Results & Impact

Real-Time Effects

Effects applied instantly during recording and preview.

Low Latency

End-to-end latency reduced to a minimal, interactive level.

High Audio Quality

MP3 export produced clear, distortion-free audio.

Smooth UI and Workflow

Users can switch effects without pauses or reprocessing.

Broad Device Compatibility

Stable performance on mid-range phones, low-end devices, and newer flagships.

Efficient Performance

Native processing reduced CPU load by 40–60% compared to Java-based implementation.

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Conclusion

By combining FFmpeg, libmp3lame, SoundTouch, and a native audio engine, we developed a high-performance real-time voice changer app for Android. The solution provides fast audio processing, smooth live previews, and professional-quality output—ideal for entertainment apps, content creators, and voice-based tools.