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Punting > Orpheus Interview > Flashcards

Orpheus Interview Flashcards

1
Q

What is an analog music source?

A

A medium in which music is played through mechanical means e.g. grooves on a vinyl / magnetic tape

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2
Q

How can you listen to the contents of an analog music source on a computer?

A

Analog material must be converted into binary data through A-D conversion - such as ripping a vinyl through serato / rekordbox / preamp & soundcard, or connecting a tape deck to a sound card.

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3
Q

What is a digital music source?

A

A source that can already be interpreted by a computer - such as an audio file (mp3, flac, wav, aif, etc..) / CD / DVD, or a streaming method through DSPs

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4
Q

List the 3 main audio file quality types

A

Uncompressed lossless, Compressed lossless, Lossy

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5
Q

List 5 points about uncompressed lossless audio formats

A
  • Complete retention of quality from original binary source (analog or digital) - highest fidelity
  • All data is treated equally in the reproduction of audio - so silence is given as many bits per second as a busy part of a track
  • Main formats include WAV and AIFF - which use Pulse Code Modulation (PCM) as the storage algorithm
  • Take up the most memory of all formats - this is why you do not stream uncompressed lossless video files online / download
  • Can be compressed into compressed lossless without any perceived loss of quality OR compressed into lossy with a potential perceived loss of quality
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6
Q

List 5 points about compressed lossless audio formats

A
  • Complete retention of quality from original binary source (to our ear) - highest fidelity
  • Unperceiveable data such as silence is given almost no bits in order to save memory and efficiently store the audio
  • Main formats include FLAC and ALAC, with FLAC being the most popular
  • Happy medium between lossy and uncompressed lossless
  • Can be uncompressed into PCM (WAV, etc..) or compressed further into lossy
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7
Q

List 4 points about lossy audio formats

A
  • Some degree of quality loss, as some audio data is negated or lost in order to save memory space (e.g. frequencies above 20kHz)
  • Main formats include mp3, aac, wma.
  • Most efficient for storage, providing sufficient quality audio for the overwhelming majority of the population with only a fraction of the memory space
  • Cannot be converted into lossless, because not all of the original source material is present (e.g. high frequencies) and cannot be recreated properly
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8
Q

Define ‘Transparent’

A

Refers to the threshold at which a lossy file is undistinguishable to a lossless file to the average listener - roughly 192kbps at a constant bitrate

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9
Q

List the accepted lossless and lossy formats on Orpheus

A

LOSSLESS: flac only, most efficient and conversion possible

LOSSY: mp3, aac (digital download, iTunes respectively) and ac3, dts (DVD material)

mp3 > aac every time unless there are exclusives in aac format from iTunes

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10
Q

What is the most popular mp3 encoder and why?

A

LAME - open source, reliable, high quality

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11
Q

When converting an audio file into mp3 with LAME, there are three options regarding how the bitrate is manifested in the output. List them

A
  • CBR (Constant Bitrate)
  • VBR (Variable Bitrate)
  • ABR (Average Bitrate)
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12
Q

Explain CBR

A
  • CBR involves setting a target bitrate at the start of conversion, in which LAME will output an mp3 with that set bitrate across the entire track.
  • This means that regardless of sound complexity, each second of music is treated and compressed in the same nature
  • Predictable file size and most uniform listening experience
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13
Q

Explain VBR and list its sub-formats

A
  • VBR involves setting a target bitrate at the start of conversion. LAME will then convert the audio into an mp3 with that target in mind, however some negative deviance from the quality will occur depending on sound complexity
  • Each second of music is treated differently depending on complexity - therefore silence is given significantly less bits per second than complex audio
  • Outcome is a file that has a general bitrate that is close to the target, but there will always be dips in quality.
  • V0 - V9. V0 = 245kbps, V2 = 190kbps (lowest acceptable on Orpheus)
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14
Q

Explain ABR

A
  • ABR involves setting a target bitrate at the start of conversion. LAME will then convert the audio into mp3 which has a varying bitrate throughout the material, but the cumulative average will always equal the target
  • Not the best method of conversion, as the variability of quality will vary depending on the nature of the source
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15
Q

Explain transcoding

A

Transcoding is the action of converting an audio format into another audio format

Bad transcodes involve working against the optimal conversion methods, and do not make sense. These involve:

  • Lossy –> Lossless
  • Same br lossy –> Same br lossy
  • High br lossy –> Low br lossy
  • Transcodes can be detected via spectral imaging and are undesirable
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16
Q

How do you navigate Orpheus?

A

BitTorrent

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17
Q

Explain how BitTorrent works, including seeding, leeching, and upload credit

A
  • BitTorrent allows users to share data with each other through .torrent files - these files are not the target files specifically, instead they refer to the target files and the source material is downloaded through different peers (users who also have the .torrent in their client) each giving small parts of data automatically
  • When you are downloading a torrent, you are leeching - once you have downloaded and continue to stream data through the .torrent, you are seeding – meaning you are giving chunks of the torrent data to other peers who are downloading the same file
  • You receive upload credit for having people leech off you, so it is beneficial to leave torrents seeding. This is a fair system where everyone works together to share files
18
Q

Explain the ratio system on Orpehus

A
  • Each user has a ratio figure. This is a weighting of how much they have uploaded compared to downloaded. A ratio of 1 implies they give as much as they take, therefore it is healthy.
  • Naturally, it can be hard to maintain a ratio like this therefore each user has a required ratio to satisfy in order to keep downloading. This figure is flexible and achievable as long as you don’t take the piss
  • The required ratio is calculated by taking into account how much data you have downloaded, as well as how many torrents you are seeding
19
Q

Explain how the required ratio system works depending on the amount of data a user has downloaded

A
  • Users have a required ratio of 0 for the first 5GB of downloads, if they do not seed anything subsequently. If they continue to seed each torrent for more than 72h per week, then they can continue to have this ratio for up to 20GB of downloads.
  • It is generally good practice to seed everything as this helps maintain a good ratio, but it also reduces your required ratio up to a certain point (100GB+)
20
Q

What happens if you dip below the required ratio?

A

Ratio watch –> 2 week period where you need to improve the ratio to above the standard. If this is not achieved then leeching privileges will be removed.

You can pull it out the bag in ratio watch by uploading new torrents, trumping files, filling requests, and seeding

If you download more than 10GB in ratio watch, you will be shut off from leeching. If you do not adhere to the upload quality rules, you will also be shut off

21
Q

Explain freeleech and neutral leech torrents

A
  • Freeleech: the data downloaded from these torrents is not counted in your ratio calculations, but your seeding data is. This is a good way to improve your ratio / maintain a good ratio
  • Neutral leech: neither data downloaded or data uploaded is counted in ratio calculations - basically a void torrent
22
Q

What is port forwarding?

A
  • Port forwarding is the process of allowing users on public internet to connect directly to your computer
  • This involves specifying a certain port and telling your modem to allow users to connect to your computer specifically
23
Q

Why is port forwarding preferable?

A

Port forwarding ensures you can connect to the entirety of the Orpheus network, and ensures that leechers can actually leech data that you are seeding.

24
Q

What are DHT’s and what are they useful for? Why do they need to be disabled for Orpheus?

A

DHT’s (Distributed Hash Tables) are a system for finding peers to connect to that do not have a centralised network - meaning it is easier to find them for downloads.

They are not allowed for Orpheus, as having them enabled for your computer allows non-users to connect and download torrents.

25
Q

When uploading a torrent to Orpheus, what should you always do and why?

A

Mark as private, to prevent non-users from accessing the material

26
Q

Why are spectral analysis tools useful?

A

To verify the quality of an audio file, as well as detect poor transcodes. Different qualities have specific characteristics when imaged.

27
Q

List the spectral characteristics of each accepted mp3 format on Orpheus, as well as lossless formats.

A 
320 CBR: 20.5khz cutoff
256 CBR: 20khz cutoff
VBR V0 (245kbps): 19.5khz cutoff
192 CBR: 19khz cutoff
VBR V2 (190kbps): 18.5khz cutoff
(all have a slight shelf at 16khz)

128 CBR: 16khz cutoff

Lossless formats are full spectrum of human hearing: so the frequency plot always reaches 22khz.

28
Q

How can you detect a transcode in a spectral imaging software?

A

Transcodes have artifacts reaching up to 22k which are not uniform. They will also have a clear shelf at the cutoff frequency of the original file (e.g. V2 190kbps - 18.5khz)

29
Q

Before spectral analysis, you need to check what bitrate or encoding algorithm the file claims to be. What software would you use?

A

MediaInfo

30
Q

Outline the difference between CD ripping and CD burning

A
  • Ripping => extracting the files (e.g. audio) from a CD

- Burning => writing the files (e.g. audio) to a blank CD

31
Q

Outline the use and role of .log and .cue files.

A
  • log files are text files which are formed after ripping a CD’s contents. They log whether any errors occurred during the process, and are used to determine whether one rip is better than another. These can be modified / doctored, but should never be done.
  • cue files store all the metadata of an existing CD, and act as a catalog of sorts. This is handy for burning an existing released CD to a blank CD (copying).
32
Q

Give an application that can be used for CD ripping and burning.

A

XLD for Mac

33
Q

Explain what dupes are.

A

A dupe is a torrent that is a duplicate of an existing torrent in terms of the material that it contains. This can involve music files with identical bitrates/format/sampling rate, year of release, label etc.

34
Q

The same music can also be considered a non-dupe. Explain when this can happen

A
  • If releases of the same album have bonus content

- If the release was released again on a different year or a different label

35
Q

Define ‘Trump’

A

Act of replacing a torrent that is insufficient with the rules / has quality issues with a better torrent that follows the rules or has a higher quality

36
Q

List the three main types of trumps.

A

Format / Tag / Folder

37
Q

Briefly outline format, tag, and folder trumps.

A
  • Format: You can format trump if you have an identical release with a higher quality bitrate/format than the existing torrent on Orpheus
  • Tag: You can tag trump if you have an identical release which has properly formatted metadata (title, album, artist, track number) and no incorrect information in comparison to the existing torrent
  • Folder: You can folder trump if you have an identical release with no nested folders, or if you have an identical release with correct folder titling
38
Q

What is the minimum quality requirement for uploading to Orpheus?

A

Any audio format (AAC, Mp3 etc) that has a bitrate average or constant to 192kbps

39
Q

What encodes can always be uploaded if there are no available torrents? (Lossy)

A
  • mp3 320 CBR / mp3 V0 VBR / mp3 V2 VBR

- AAC, if the release has iTunes exclusive media

40
Q

List the 4 lossless format trump rules.

A
  • FLAC uploads must be ripped directly from official sources and releases, no subsequent rips (unless the official release was a rip from source)
  • Any FLAC with a .log file can format trump a FLAC without one
  • A FLAC with a 100% ripping quality score can format trump one with a score that is less than 100% - however the score must be 100%: if the score x < 100, then it cannot format trump
  • A FLAC with a 100% ripping .log and no .cue file can only be trumped with a FLAC with a 100% ripping .log and a genuine .cue file
41
Q

Outline what a tag trump involves.

A

Correcting an existing torrent file that has missing metadata such as track title, album, artist, or track number - or there are grave misspellings in the cataloguing.

  • Also, if a torrent is formatted all in lower case, it is trumpable
42
Q

Outline what a folder trump involves.

A
  • Folder trumping is to do with the actual contents of the .torrent file, rather than the download file itself
  • For a trump to occur, the material inside must be missing information such as artist, album, year, or source format. Additionally - the track titles inside the folder must be titled correctly
  • Also occurs if there are compressed folders or nested folders inside the downloaded torrent

Punting (3 decks)

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