What it does
The Tascam Porta Two Ministudio was a 4-track cassette recorder released in 1985. Compact, affordable, and gloriously imperfect — it defined the sound of countless bedroom recordings. Its preamp clipped early and unapologetically, its transport wobbled, and its tape hissed. That's the point.
PortaTwin captures its full signal chain — the way the preamp colors and saturates, the wow and flutter of an aging transport, the hiss and bandwidth loss of worn tape. It works as a subtle analog glue or as a full lo-fi destruction unit. Everything in between is fair game.
Signal flow
Input → HPF 10Hz → Preamp Gain (CLEAN / HOT) → EQ Low Shelf 483Hz → EQ High Shelf 8840Hz → [if TAPE IN on]: Tape Saturation (B-H curve) → Head Bump → Wow/Flutter → Hiss → (repeat N times based on WEAR — saturation + hiss + HF loss only) → Output Level (log fader) → DC Blocker [BYPASS skips everything]
Preamp
| Parameter | Range | Default | Description |
|---|---|---|---|
| INPUT | 0–1 | 0.5 | Input gain with cubic curve ×8.0. Unity gain at center. |
| EQ LOW | 0–1 | 0.5 | Low shelf EQ at 483 Hz, ±12 dB. |
| EQ HIGH | 0–1 | 0.5 | High shelf EQ at 8840 Hz, ±12 dB. |
| CLEAN / HOT | toggle | CLEAN | Preamp character mode. |
Transparent linear gain. Good for subtle coloring without added character.
Double tanh saturation modeled on LM833 op-amp character. The gain pushes through two saturation stages — one before the EQ, one after. The harder you push INPUT, the more harmonic distortion you get. This is what happens when you push the input fader on the real machine past its comfort zone.
Tape
| Parameter | Range | Default | Description |
|---|---|---|---|
| TAPE DRIVE | 0–1 | 0.0 | Tape saturation amount (B-H curve with bias interaction). |
| WOW/FLT | 0–1 | 0.0 | Pitch modulation from transport irregularities. |
| WEAR | 0–1 | 0.0 | Tape degradation macro (hiss + passes + HF loss). |
| BIAS | 0–1 | 0.5 | Tape bias offset — changes saturation color and knee. |
| SPEED | toggle | 3¾ips | Tape speed: 3¾ips or 1⅞ips. |
| TAPE IN | toggle | on | Bypasses the entire tape section when off. |
Realistic B-H curve tape saturation with bias interaction. At low settings, adds warmth and subtle compression. At high settings, the tape clips harmonically. Head bump at ~200 Hz adds low-end presence proportional to drive.
Multi-LFO pitch modulation system. Applied on the first tape pass only — physically correct, as wow and flutter are transport phenomena (motor, rollers), not tape phenomena.
- Wow: main oscillator at 0.85 Hz + two sub-harmonics (×1.73 and ×0.63). Max depth 3 ms
- Flutter: three LFOs at 4.8, 6.3, and 8.1 Hz. Max depth 0.3 ms
- Random drift: filtered noise, very slow movement. Max depth 0.8 ms
A macro that simultaneously controls multiple degradation axes:
- Hiss level — rises early with a convex curve
- Number of tape passes: 1 pass (0–25%) up to 8 passes (88–100%)
- High frequency loss down to 4 kHz floor
- Additional low-pass filtering on extra passes
- Extra passes apply saturation, hiss, and HF loss only — no additional wow/flutter
Shifts the operating point of the tape saturation. Center (0.5) is neutral with a knee of ~0.525. Higher values add warmth and even harmonics. Lower values increase odd harmonics and edge. Also affects HF shelf response and noise floor.
Physically models the difference between tape speeds. Not just a filter — the slower speed means more relative transport instability and noise.
- At 1⅞ips: wow/flutter intensity ×1.6, hiss ×1.6, bandwidth reduced to 8 kHz
- Head bump frequency shifts to ~130 Hz
Output
| Parameter | Range | Default | Description |
|---|---|---|---|
| OUTPUT | 0–1 | 0.842 | Output level, logarithmic fader curve (−60 dB to +12 dB). |
| BLEND | 0–1 | 1.0 | Scales all tape effect intensities (DRY to WET). |
| BYPASS | toggle | off | Full bypass, raw signal passthrough. |
| AUTO GAIN | toggle | off | Automatic gain compensation for preamp and tape processing. |
Logarithmic fader with a −60 dB to +12 dB range. Mute zone below 5% of fader travel. Unity gain (0 dB) at ~84% of the fader travel. Behaves like a real console fader with most resolution in the mixing zone.
Scales the intensity of all tape effects simultaneously (tape drive, wow/flutter depth, hiss level). This is not a dry/wet mix — it operates within a single signal path to avoid comb filtering. At DRY (0): preamp + EQ only. At WET (1): full tape processing.
RMS measurement calibrated at 0 VU = −14 dBFS (consumer/−10 dBV standard, matching the Porta Two). Spring-damper needle physics (spring=155, damping=20) with ~300 ms rise time and ~1.5% overshoot, per IEC 60268-17.
All 14 parameters are automatable.
Design notes
BLEND scales effects, not mix. A traditional dry/wet mix causes comb filtering because the wow/flutter delay buffer shifts the wet signal in time. Instead, BLEND scales the intensity of effects within a single signal path — the standard approach used by professional tape emulation plugins.
Wow/flutter is a transport phenomenon, not a tape phenomenon. Extra passes from WEAR apply tape degradation (saturation, hiss, HF loss) but do not re-apply wow/flutter. Physically correct: wow and flutter come from the motor and rollers, not from the oxide coating.
WEAR and WOW/FLT are independent axes. A tape can have a perfect transport mechanism but degraded oxide (high WEAR, no WOW/FLT), or vice versa. These are separate physical phenomena and are treated as such.
CLEAN/HOT replaces a separate drive knob. On the real Porta Two there is no "drive" control — saturation happens when you push the input into the preamp. HOT mode models this behavior. The harder you push INPUT, the more saturated the result.
Logarithmic output fader. True logarithmic curve (−60 dB to +12 dB) like a real console fader, with most of the resolution concentrated in the mixing zone (−30 to −10 dB).
Version history
| v0.9 | Rebranded as PA PortaTwin. Blend redesigned as intensity scaler (zero phasing). Wow/flutter first-pass only. Logarithmic output fader (−60 to +12 dB). VU calibrated at −14 dBFS with updated physics. Input gain curve ×8 for unity at center. New panel artwork, multi-color knobs per section. |
| v4.5 | Fixed wow/flutter delay buffer always-feed; added crossfade dry→wet; fixed auto gain with per-sample smoothing and simulation-based compensation. |
| v4.3 | Fixed BLEND phasing (single signal path), doubled wow/flutter depths, system VST3 install, pkg installer. |
| v4.0 | Major restructure: CLEAN/HOT, TAPE DRIVE + WOW/FLT + WEAR + BIAS, BLEND, GUI 900×420. |
| v3 | Added TAPE IN, BYPASS, VU meter physics. Pointless Audio branding. |
| v1–v2 | Initial release. |