# Tube Preamp Saturation Add single-ended tube-preamp coloration: an asymmetric waveshaper whose bias control sets the even-harmonic warmth, with drive, tone tilt, dry/wet mix and output trim. > Canonical page: https://elysiatools.com/en/tools/audio-tube-preamp-saturation - **Category:** Media - **Keywords:** tube saturation, tube preamp, triode, even harmonics, second harmonic, asymmetric waveshaper, tanh, warmth, valve, drive bias ## Overview Models the stage saturation plugins actually imitate: a single-ended triode preamp running into its curved region. The waveshaper is y = (tanh(K·(x+B)) − tanh(K·B)) / (K·(1−tanh²(K·B))) evaluated per channel with FFmpeg aeval val(ch) expressions — a biased tanh with unity small-signal gain, so quiet material passes clean while loud peaks bend into the curve. The bias B (0–0.4) is the even/odd balance: any asymmetric curve generates even-order harmonics (2nd, 4th — octave-related and consonant) alongside the odd ones, and bias sets how far the operating point sits off center; 0 gives a symmetric tanh with purely odd harmonics, higher values tilt toward the 2nd-harmonic warmth single-ended stages are famous for (push-pull stages cancel exactly these components by design). The curve runs inside a 2× oversampled chain (resample to 96 kHz, shape, back down) so the harmonics the shaper sprouts do not fold back into the audio band as aliasing; a 20 Hz high-pass removes the DC offset the biased curve naturally produces. Drive (1–10) is pre-gain into the curve, compensated after so overall gain stays near unity; a post-shaper tone switch adds a gentle warm or bright shelf; mix blends the shaped signal against the untouched dry path for parallel saturation; output gain trims ±12 dB and a limiter guards the sum. Before/after, an FFT probe measures the harmonic growth in the 300–900 Hz and 8.5–11.5 kHz zones plus RMS/peak/crest-factor deltas — crest factor falling a few dB while RMS holds is the visible fingerprint of saturation. ## Inputs - **Audio file** (file) - **Drive** (number) - **Bias** (number) - **Tone** (select) - **Mix (%)** (number) - **Output gain (dB)** (number) - **Output format** (select) ## When to use - Adding musical even-order harmonics and analog warmth to sterile digital recordings or synth tracks. - Controlling transient spikes and reducing crest factor naturally without conventional hard clipping. - Applying parallel tube saturation to drum stems or vocal tracks to thicken low-mids while retaining punch. ## How it works - Upload an audio file and set the drive parameter to control input pre-gain into the waveshaper curve with automatic output compensation. - Adjust the bias control from 0 (symmetric tanh with odd harmonics) up to 0.4 to introduce rich second-order and even-order harmonics characteristic of single-ended tube stages. - The audio processes through a 2× oversampled internal path at 96 kHz with a 20 Hz high-pass filter to prevent DC offset and aliasing distortion. - Fine-tune the post-shaper tone switch (warm, neutral, or bright), dry/wet mix percentage, and output gain trim before exporting to MP3, WAV, FLAC, M4A, or OGG. ## Use cases - Bass and Synth Thickening: Dial in bias 0.15–0.25 and moderate drive to generate an octave harmonic that cuts through small speakers. - Vocal Warmth and Presence: Apply subtle drive with a warm or bright tone shelf and an 80% wet mix to soften sibilance and add richness. - Drum Bus Parallel Glue: Run high drive (7–9) at 40–60% dry/wet mix to add density and sustained body while preserving snappy transients. ## Frequently asked questions ### What does the bias parameter do? Bias shifts the waveshaper's operating point off-center. A setting of 0 produces symmetric odd harmonics, while higher values (up to 0.4) generate warm, consonant even-order harmonics like the second harmonic. ### How is aliasing prevented during heavy saturation? Processing runs through a 2× oversampled processing chain up to 96 kHz before folding back down, preventing upper harmonic multiples from reflecting as inharmonic digital aliasing. ### Does increasing drive drastically boost the audio level? No, the tool incorporates post-shaping gain compensation to keep overall signal levels close to unity before applying manual output gain trims. ### Why is there a built-in 20 Hz high-pass filter? Asymmetric waveshaping naturally creates a slight DC offset in the waveform, which the 20 Hz filter removes to protect headroom and downstream equipment. ### What audio formats can I export? You can export the saturated audio file directly into MP3, WAV, FLAC, M4A, or OGG Vorbis formats. ## Related tools - [Audio Mixer](https://elysiatools.com/en/tools/audio-mixer): Mix two audio files together with customizable timing control - [Audio Codec Swap](https://elysiatools.com/en/tools/audio-codec-swap): Change the codec of an audio file within a chosen output format - [Audio Vocoder](https://elysiatools.com/en/tools/audio-vocoder): Apply a vocoder effect using a carrier and modulator - [Batch WAV Audio Converter](https://elysiatools.com/en/tools/batch-wav-converter): Convert multiple WAV files to OGG, AAC, M4A, and OPUS formats with quality settings, bitrate control, and batch processing - [Batch Audio Converter](https://elysiatools.com/en/tools/audio-batch-converter): Convert multiple audio files between different formats like MP3, WAV, FLAC, AAC, OGG, Opus with quality settings and batch processing - [Audio Bit Depth Reducer](https://elysiatools.com/en/tools/audio-bit-depth-reducer): Reduce the bit depth of an audio file (e.g., 24-bit to 16-bit) - [Audio Chord Progression Detector](https://elysiatools.com/en/tools/audio-chord-progression-detector): Estimate an audio file's chord sequence locally and download CSV, JSON, SVG, and method notes in one ZIP. - [Audio Format Converter](https://elysiatools.com/en/tools/audio-converter): Convert audio files between different formats like MP3, WAV, FLAC, AAC, OGG with quality settings and volume adjustment ## Samples - [Copyright-Free MP3 Audio Samples](https://elysiatools.com/en/samples/mp3-samples): Collection of royalty-free audio samples for testing and development purposes including nature sounds, meditation music, and ambient audio - [Copyright-Free WAV Audio Samples](https://elysiatools.com/en/samples/wav-samples): Uncompressed PCM WAV audio samples for testing and development, mirrored from MP3 set with nature sounds and meditation music - [Copyright-Free Raw PCM Audio Samples](https://elysiatools.com/en/samples/pcm-samples): Raw PCM s16le audio samples featuring nature ambience and relaxing music for waveform, playback, and conversion workflows - [Speech Learning & Safety Audio Samples](https://elysiatools.com/en/samples/audio-learning-safety-samples): Deterministic synthetic WAV inputs for pronunciation comparison, dictation preflight, alert degradation, and voice privacy tools.