HiFi Decode

HiFi Audio Decoding

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Capture

Please consult the Hardware Installation Guide for installation of RF Taps.

HiFi FM signals can be captured with just about any basic SDR or ADC system, as its incredibly low bandwidth compared to video signal, however how you tap HiFi audio varies per format.

Caution

• LaserDisc, Video8/Hi8 & Betamax NTSC are single channel FM RF formats, i.e DdD is suitable for use capturing.

• VHS, Betamax PAL and other formats require multiple ADC channels for Video RF & HiFi audio (and Baseband or Linear audio)

• Umatic & SMPTE and other broadcast formats require an ADC for Video RF but also requires standard audio ADC's for Linear Timecode & audio tracks.

• Betacam & W-VHS require duel ADC's for the video tracks alongside the above-mentioned for audio.

Please look at the Clockgen Mod & the new MISRC which provides synchronised at the clock source level capturing of multiple channels of signals.

Tip

This page is for the full HiFi decoder, for real-time decoding you want to look at the RTLSDR Decode page aimed at VHS users.

Supported Formats

• VHS & SVHS
• Video8 & Hi8

Note

Sony 8mm Video8/Hi8 can have PCM Digital which can only be captured with a Digital8 camcorder/deck but HiFi FM is the standard audio format and captured alongside Video/Timecode as they are on different carriers.

Note

PAL Video8, and Betamax decoding are still work in progress, with VHS PAL/NTSC having slightly better than hardware support for stable in-spec media.

Warning

On some VHS (NTSC/PAL) decks with A.Out is a baseband audio (Linear) test point, not HiFi RF.

Supported Features

• Noise Reduction (Based on IEC60774-2/1999)
• Variable Sample Rate Input
• Amplitude (Gain) Control
• Multiple Tape Formats

HiFi Decode

HiFi decode converts the FM signal into standard digital audio in a simple 1-command decode workflow.

RF Input --> Demodulation --> Optional Noise Reduction --> 48khz 24bit FLAC Audio File

FLAC Compressed & RAW Uncompressed Captures 8-bit or 16-bit are supported.

Usage

Note

samplerate & sounddevice should be installed for Linux builds to work properly (if not automatically installed).

Infile RF Data, outfile Audio Data must have .wav or .flac extension at the end otherwise it will be an extension-less output and your default system audio player will not open the file automatically for example.

Example Usage Command

Linux/MacOS

hifi-decode -t 8 -p -f 40 --audio_rate 48000 HiFI-Audio-PAL-DdD.s16 hifi-decode-output.flac

Windows

decode.exe hifi --threads 8 --system pal --audio_rate 48000 --frequency 40 HiFI-Audio-PAL-DdD.s16 hifi-decode-output.flac

With GUI

decode.exe hifi --gui input.u8 output.flac

TV System

--system pal / ntsc

-n - NTSC

-p - PAL

Input Sample Rate Commands

-f Manual Input Hz, Mhz, Ghz.

--frequency

-f 40 - DomesDay Duplicator (DdD)

-f 8 - RTLSDR

-f 10 - CX Card Clock Gen Setup

For CX Card Captures:

--cxadc 28.6 MHz/8-bit (8fsc)

--cxadc3 35.8 MHz/8-bit (10fsc)

--10cxadc 14.3 MHz/16-bit (4fsc) (Technically 4fsc NTSC)

--10cxadc3 17.9 MHz/16-bit (5fsc) (Technically 4fsc PAL)

HiFi Decode Control Options

--audio_rate Audio rate in Hz i.g 44100, 48000, 96000, 192000 (48Khz Default)

---

--audio_mode Audio mode:

• s stereo
• mpx stereo with mpx
• l left channel
• r right channel
• sum mono sum

---

--gain Sets Amplitude size/volume useful for avoiding clipping. (i.g 0.5 = 50%) (default is 1.0)

--gui Opens Graphical User Interface (can require input file and output file name to be set)

--bg Forces guessing of the carrier bias.

-t To set the threads for parallel decoding. (Can support real-time with enough threads)

--original To force the use of vhs-decodes fm demodulation.

--preview Enables a faster decoder for real-time preview. (faster and noisier)

--noise_reduction NOISE_REDUCTION Set noise reduction on/off (default is on)

--auto_fine_tune AUTO_FINE_TUNE Set auto-tuning of the analogue front end on/off (useful for mixed standards tapes, but may cause issues with 8mm formats.)

--NR_sidechain_gain Sets the noise reduction envelope tracking sidechain gain (default is 33). Range (20~100): 100 being a hard gate effect, operating range should be 40 and below (dynamic range decompressor adjustment smaller = more aggressive)

--8mm Sony 8mm formats, Video8 & Hi8 HiFi FM.

--gnuradio Opens ZMQ REP pipe to GNURadio at port 5555, the sample rate for GNURadio is 8388608 Hz

--overwrite Overwrites local file if named file already exists.

HiFi Decode Output Formats

Recommended Standard Format 48khz.

Sample Rate	Bit Depth	Codec	Container
192khz	24-bit	FLAC	.FLAC
96khz	24-bit	FLAC	.FLAC
48khz	24-bit	FLAC	.FLAC
44.1khz	24-bit	FLAC	.FLAC

HiFi Decode Notes

HiFi is recorded within a defined limited range the further it deviates from that range the more likely it is to have or cause interference with the luminance channel.

With --bg you will see something like the following as it guesses and finds the L/R carriers.

L carrier found at 1.65 MHz, R carrier found at 1.80 MHz

Standard Output

- Decoding speed: 3063 kFrames/s (0.19x)
- Audio position: 0:00:01.349
- Wall time     : 0:00:07.048
Progress [#                                       ] 1.93%

Good Calibration / Tape In Spec

- Decoding speed: 2637 kFrames/s (0.16x)
- Audio position: 0:01:02.014
- Wall time     : 0:06:16.213
Bias L 7.27 kHz, R 0.10 kHz (good player/recorder calibration)
Progress [##################################      ] 85.16%

Bad Calibration / Tape Recorded Out of Spec

 Decoding speed: 2627 kFrames/s (0.16x)
 Audio position: 0:00:12.055
 Wall time     : 0:01:13.427
ias L -10.00 kHz, R -10.00 kHz
ARN: the player or the recorder may be uncalibrated and/or
he standard and/or the sample rate specified are wrong
Progress [#######                                 ] 16.62%%

For example, in a badly calibrated VCR, the left channel is noisy and the right is clean, you can check this by selecting left or right playback in VLC with quick test captures.

You can fix this by adjusting tracking as you would normally for video and fine-adjusting pots on higher-end VCRs.

There is also the Videomem's original tool for inspection and tinkering

VideoMem's Superheterodyne Decoding Tools a GNU Radio script-based HiFi decoding tool. (Ouputs 16-bit 192khz PCM)

Post Processing Recommendations?

The EBU R128 Standard or -11 LUFS normalisation is recommended as its widely used in broadcast/online production this can be done with StaxRip or with FFmpeg tools.

De-poping can be done very effectively with modern tools like iZotope RX.

PCM Audio

Video8/Hi8 Could have PCM audio to extract this Digital8 and DV25 FireWire transfer is recommended.

For PCM data in video streams you can decode it with SDVPCM Decoder

Older Version Notes

DomesDay Duplicator Users:

Note: You need to use FLAC compressed or capture in 16-bit singed .raw and rename it to .s16, if capturing in 10-bit packed .lds, due to lack of ld-lds-converter integration the files not decode and will require being FLAC compressed to 16-bit or 8-bit standard format data.

ld-lds-converter -u input.lds --debug --unpack --input input.lds --output output_40msps_16-bit.s16

To unpack your capture to 16-bit singed, this is very much worth noting for Video8/Hi8 users with 1 RF capture file.

Using FLAC Compressed Captures Via Pipe

ld-ldf-reader input-hifi.flac | hifi-decode - --pal -f 40 --audio_rate 48000 Decoded_Output.flac

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