I read an article about how magnetic tape in the early 1960's could only record roughly 100kbs. Does this mean the master recordings of the Beatles are relatively low quality compared to the 768kbs (16 bit by 48 kHz) that cds use today? I know some of their music was recorded on vinyl record. Does anyone know what equivalent bit rate of those records would be?
3 Answers
Looking at the specs of the IBM 2401 tape drive from that era, you can see it's at least more complicated than that. The fastest of the 3 models recorded 90 kbyte/s while running the tape at 112.5 inch/s (and you thought a 15 inch/s tape recorder was fast), and the data rate rose with tape speed.
That does not mean this was the limit of the medium, though. Tape drives were often used for long-term storage, so the format was designed to be readable even when the tape degraded: they allocated a lot of physical space for each bit so it'd remain readable if there were physical defects on the tape (dropouts).
The specs for a multitrack audio recorder from that era shows what's possible if you use the tape to its limits. The Telefunken M15 was the direct successor to the M10a that appears to have been used for several Beatles records.
Frequency response: 30Hz to 16kHz (15 ips)
Signal to Noise Ratio: 65dB
This is roughly equivalent to 32-36 kHz sampling at 11 bits. That's a data rate of 36k x 2 x 11 = 792 kbit/s for 2 channels. CD is 1411 kbit/s of audio, plus some error correction and other data.
I don't think the Beatles ever recorded directly to vinyl, the article indicates they used tape decks. These would have been used for the mastering process, with vinyl as the end product only.
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@justaboy4 I rejected your edit. The Red Book specification for CD audio does include error correction (cross-interleaved Reed–Solomon coding, CIRC) and other data (8 subcode channels).– HobbesCommented Apr 29 at 9:27
The article you read has either been misinterpreted or was monstrously misleading. It is possible that what they were referring to was the fact that the frequency response required from an analogue medium was only enough to record 100kB/s of digital information. That does not mean that the recording quality of the original recording was equivalent to a digital recording of that bandwidth. Such a conclusion is entirely incorrect.
The Beatles were originally recorded using analogue tape technology. The frequency response of the analogue tape machinery that was used is entirely independent of any digital sampling bitrate that might be used in the future to encode such a recording.
Recordings done way before the Beatles were performing still stand up to scrutiny today as extremely high-quality recordings.
You should be sure to understand the difference between analogue and digital recording techniques. With analogue, the microphone, preamp, recording media and reproduction circuit are all significant contributors to the signal path. With digital audio everything between the Analogue to Digital Converters and the Digital to Analogue Converters is simply a matter of data storage and transmission.
There is no way to compare them because one is analog and one is digital. The way to calculate kbps is:
bit depth * sample rate * channels
Neither vinyl nor cassettes use bit depth or sample rates. The best you can try to compare is the similarity between bit depth of the CD and dynamic range of the cassette or vinyl
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That's incorrect. There is a fairly simple way to compare the two: the sample rate directly translates to the bandwidth of the recording (44 kHz sampling = 20 kHz bandwidth), and the bit depth tells you the SNR (1 bit = 6 dB of SNR, if we ignore noise shaping).– HobbesCommented Sep 20, 2019 at 7:10
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@Hobbes although that is true I would say that it is the same as asking what the equivalent pixel density is of an original Van Gogh painting is. You can compare the aspect ratio and canvas size but you are not going to calculate ppi.– TimKCommented Sep 20, 2019 at 8:14
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that's not the same though. Audio reproduction is governed by the Shannon-Nyquist sampling theorem, and you can build an AD-DA chain that perfectly reproduces the original signal. For visual media, we're far away from being able to do that because you'd have to scan individual atoms to get a perfect reproduction.– HobbesCommented Sep 20, 2019 at 8:32
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@Hobbes well you should answer the question and tell him the bit rate equivalent of the original Beatles recordings.– TimKCommented Sep 20, 2019 at 9:43