Editing VHS (section)

=== Audio recording ===

After leaving the head drum, the tape passes over the stationary audio and control head. This records a control track at the bottom edge of the tape, and one or two linear audio tracks along the top edge.<ref name="poptronics" />

==== Original linear audio system ====
In the original VHS specification, audio was recorded as [[baseband]] in a single linear track, at the upper edge of the tape, similar to how an audio [[compact cassette]] operates. The recorded frequency range was dependent on the linear tape speed. For the VHS SP mode, which already uses a lower tape speed than the compact cassette, this resulted in a mediocre frequency response<ref name="poptronics" /> of roughly 100&nbsp;Hz to 10&nbsp;kHz for NTSC,{{citation needed|date=March 2014}} frequency response for PAL VHS with its lower standard tape speed was somewhat worse of about 80&nbsp;Hz to 8&nbsp;kHz. The [[signal-to-noise ratio]] (SNR) was an acceptable 42&nbsp;dB for NTSC and 41&nbsp;dB for PAL. Both parameters degraded significantly with VHS's longer play modes, with EP/NTSC frequency response peaking at 4&nbsp;kHz. S-VHS tapes can give better audio (and video) quality, because the tapes are designed to have almost twice the bandwidth of VHS at the same speed.

Sound cannot be recorded on a VHS tape without recording a video signal because the video signal is used to generate the control track pulses which effectively regulate the tape speed on playback. Even in the audio dubbing mode, a valid video recording (control track signal) must be present on the tape for audio to be correctly recorded. If there is no video signal to the VCR input during recording, most later VCRs will record black video and generate a control track while the sound is being recorded. Some early VCRs record audio without a control track signal; this is of little use, because the absence of a signal from the control track means that the linear tape speed is irregular during playback.<ref name="poptronics" />

More sophisticated VCRs offer stereo audio recording and playback. Linear stereo fits two independent channels in the same space as the original mono audiotrack. While this approach preserves acceptable backward compatibility with monoaural audio heads, the splitting of the audio track degrades the audio's signal-to-noise ratio, causing objectionable tape hiss at normal listening volume. To counteract the hiss, linear stereo VHS VCRs use [[Dolby noise-reduction system|Dolby B noise reduction]] for recording and playback. This dynamically boosts the high frequencies of the audio program on the recorded medium, improving its signal strength relative to the tape's background noise floor, then attenuates the high frequencies during playback. Dolby-encoded program material exhibits a high-frequency emphasis when played on non-Hi-Fi VCRs that are not equipped with the matching Dolby Noise Reduction decoder, although this may actually improve the sound quality of non-Hi-Fi VCRs, especially at the slower recording speeds.

High-end consumer recorders take advantage of the linear nature of the audio track, as the audio track could be erased and recorded without disturbing the video portion of the recorded signal. Hence, "audio dubbing" and "video dubbing", where either the audio or video is re-recorded on tape (without disturbing the other), were supported features on [[wikt:prosumer#Etymology 2|prosumer]] [[linear video editing]]-decks. Without dubbing capability, an audio or video edit could not be done in-place on master cassette, and requires the editing output be captured to another tape, incurring generational loss.

Studio film releases began to emerge with linear stereo audiotracks in 1982. From that point, nearly every home video release by Hollywood featured a Dolby-encoded linear stereo audiotrack. However, linear stereo was never popular with equipment makers or consumers.

==== Tracking adjustment and index marking ====
Another linear [[control track|''control'' track]] at the tape's lower edge holds pulses that mark the beginning of every frame of video; these are used to fine-tune the tape speed during playback, so that the high speed rotating heads remained exactly on their helical tracks rather than somewhere between two adjacent tracks (known as "[[video tape tracking|tracking]]"). Since good tracking depends on precise distances between the rotating drum and the fixed control/audio head reading the linear tracks, which usually varies by a couple of micrometers between machines due to manufacturing tolerances, most VCRs offer tracking adjustment, either manual or automatic, to correct such mismatches.

The control track is also used to hold ''index marks'', which were normally written at the beginning of each recording session, and can be found using the VCR's ''index search'' function: this will fast-wind forward or backward to the ''n''th specified index mark, and resume playback from there. At times, higher-end VCRs provided functions for the user to manually add and remove these marks.<ref>{{cite web|url=http://www.crutchfield.com/S-PFiOFC1Dt8s/learn/learningcenter/home/vcr_glossary.html|title=VCRs Glossary|author=Loren Barstow|work=Crutchfield|access-date=2014-07-30|archive-date=2014-08-12|archive-url=https://web.archive.org/web/20140812193000/http://www.crutchfield.com/S-PFiOFC1Dt8s/learn/learningcenter/home/vcr_glossary.html|url-status=dead}}</ref><ref>[http://www.retrevo.com/support/JVC-HR-S7300U-VCRs-manual/id/318ag718/t/2/ JVC HR-S7300 manual] {{Webarchive|url=https://web.archive.org/web/20140810142541/http://www.retrevo.com/support/JVC-HR-S7300U-VCRs-manual/id/318ag718/t/2/ |date=2014-08-10 }}: features list: ''"..., Index Search, Manual Index Mark/Erase ..."''</ref>

By the late 1990s, some high-end VCRs offered more sophisticated indexing. For example, Panasonic's Tape Library system assigned an ID number to each cassette, and logged recording information (channel, date, time and optional program title entered by the user) both on the cassette and in the VCR's memory for up to 900 recordings (600 with titles).<ref>[https://archive.today/20120729233622/http://www.elektroda.pl/rtvforum/instrukcjeobslugi?id=2176 Panasonic Video Cassette Recorder NV-HS960 Series Operating Instructions], VQT8880, Matsushita Electric Industrial Co., Ltd.</ref>

==== Hi-Fi audio system ====
Around 1984, JVC added ''Hi-Fi'' audio to VHS (model HR-D725U, in response to Betamax's introduction of Beta Hi-Fi.) Both VHS Hi-Fi and Betamax Hi-Fi delivered flat full-range frequency response (20&nbsp;Hz to 20&nbsp;kHz), excellent 70&nbsp;dB [[signal-to-noise ratio]] (in consumer space, second only to the [[compact disc]]), [[dynamic range]] of 90&nbsp;dB, and [[professional audio]]-grade channel separation (more than 70&nbsp;dB). VHS Hi-Fi audio is achieved by using audio frequency modulation (AFM), modulating the two stereo channels (L, R) on two different frequency-modulated carriers and embedding the combined modulated audio signal pair into the video signal. To avoid crosstalk and interference from the primary video carrier, VHS's implementation of AFM relied on a form of magnetic recording called ''depth [[multiplexing]]''. The modulated [[Sound recording and reproduction|audio]] carrier pair was placed in the hitherto-unused frequency range between the luminance and the color carrier (below 1.6&nbsp;MHz), and recorded first. Subsequently, the video head erases and re-records the video signal (combined luminance and color signal) over the same tape surface, but the video signal's higher center frequency results in a shallower magnetization of the tape, allowing both the video and residual AFM audio signal to coexist on tape. (PAL versions of Beta Hi-Fi use this same technique). During playback, VHS Hi-Fi recovers the depth-recorded AFM signal by subtracting the audio head's signal (which contains the AFM signal contaminated by a weak image of the video signal) from the video head's signal (which contains only the video signal), then demodulates the left and right audio channels from their respective frequency carriers. The result of the complex process was audio of high fidelity, which was uniformly solid across all tape-speeds (EP, LP or SP.) Since JVC had gone through the complexity of ensuring Hi-Fi's backward compatibility with non-Hi-Fi VCRs, virtually all studio home video releases produced after this time contained Hi-Fi audio tracks, in addition to the linear audio track. Under normal circumstances, all Hi-Fi VHS VCRs will record Hi-Fi and linear audio simultaneously to ensure compatibility with VCRs without Hi-Fi playback, though only early high-end Hi-Fi machines provided linear stereo compatibility.

The sound quality of Hi-Fi VHS stereo is comparable to some extent to the quality of [[Compact disc|CD]] audio, particularly when recordings were made on high-end or professional VHS machines that have a manual audio recording level control. This high quality compared to other consumer audio recording formats such as [[compact cassette]] attracted the attention of amateur and hobbyist recording artists. [[Home recording]] enthusiasts occasionally recorded high quality stereo [[Audio mixing (recorded music)|mixdown]]s and [[master recordings]] from [[multitrack recording|multitrack]] audio tape onto consumer-level Hi-Fi VCRs. However, because the VHS Hi-Fi recording process is intertwined with the VCR's video-recording function, advanced editing functions such as audio-only or video-only dubbing are impossible. A short-lived alternative to the HiFi feature for recording mixdowns of hobbyist audio-only projects was a [[PCM adaptor]] so that high-bandwidth digital video could use a grid of black-and-white dots on an analog video carrier to give pro-grade digital sounds though [[Digital Audio Tape|DAT]] tapes made this obsolete.

Some VHS decks also had a "simulcast" switch, allowing users to record an external audio input along with off-air pictures. Some televised concerts offered a stereo simulcast soundtrack on FM radio and as such, events like ''[[Live Aid]]'' were recorded by thousands of people with a full stereo soundtrack despite the fact that stereo TV broadcasts were some years off (especially in regions that adopted [[NICAM]]). Other examples of this included network television shows such as ''[[Friday Night Videos]]'' and [[MTV]] for its first few years in existence. Likewise, some countries, most notably [[South Africa]], provided alternate language audio tracks for TV programming through an FM radio simulcast.

The considerable complexity and additional hardware limited VHS Hi-Fi to high-end decks for many years. While linear stereo all but disappeared from home VHS decks, it was not until the 1990s that Hi-Fi became a more common feature on VHS decks. Even then, most customers were unaware of its significance and merely enjoyed the better audio performance of the newer decks. VHS Hi-Fi audio has been standardized in IEC 60774-2.<ref>{{Cite web |title=Helical-scan video tape cassette system using 12,65 mm (0,5 in) magnetic tape on type VHS – Part 2: FM audio recording |url=https://webstore.iec.ch/preview/info_iec60774-2%7Bed1.0%7Db.pdf |website=webstore.iec.ch}}</ref>

===== Issues with Hi-Fi audio =====
Due to the path followed by the video and Hi-Fi audio heads being striped and discontinuous—unlike that of the linear audio track—head-switching is required to provide a continuous audio signal. While the video signal can easily hide the head-switching point in the invisible vertical retrace section of the signal, so that the exact switching point is not very important, the same is obviously not possible with a continuous audio signal that has no inaudible sections. Hi-Fi audio is thus dependent on a much more exact alignment of the head switching point than is required for non-HiFi VHS machines. Misalignments may lead to imperfect joining of the signal, resulting in low-pitched buzzing.<ref name="stason">{{cite web|url=http://stason.org/TULARC/entertainment/audio/general/14-18-Is-VHS-Hi-Fi-sound-perfect-Is-Beta-Hi-Fi-sound-perfec.html14.18|title=14.18 Is VHS Hi-Fi sound perfect? Is Beta Hi-Fi sound perfect?|work=stason.org | access-date=August 6, 2019}}</ref> The problem is known as "head chatter", and tends to increase as the audio heads wear down.

Another issue that made VHS Hi-Fi imperfect for music is the inaccurate reproduction of levels (softer and louder) which are not re-created as the original source.<ref name="stason"/>