Recording Audio
Note: We suggest that you keep this document open in Safari, and refer to it while you perform the recording procedure.
The first step in the Pure Vinyl workflow involves recording audio using the Pure Vinyl Recorder. You may use nearly any audio file with the Pure Vinyl editor, but there are several advantages to using the Pure Vinyl Recorder as a source of audio files:
- Automatic Decimation (Downsampling) of high sample rates If you are recording audio using a sample rate greater than 44.1 kHz (CD quality), Pure Vinyl optionally can automatically record a separate, CD quality (44.1 kHz) audio file, using a choice of several available decimation routines. The advantage to decimating while recording is that surplus CPU resources can be used to perform the decimation, with a net gain in productivity (no need to perform a separate decimation step; although decimation of audio also is possible later, from within the Pure Vinyl editor application). Decimation, performed properly, is a computationally intensive, very slow process (only 1 to 6 times realtime with the Macintosh computers available at the time of this writing). Therefore, decimating while recording can be a tremendous timesaver when it comes to creating tracks for CD. Please see this page for technical information on the decimation process used by Pure Vinyl.
- Noise Gate Recording Trigger The noise gate has a single function: detecting the drop or lift of the record stylus (or presence or absence of an audio signal of interest). On a stylus drop, recording commences (with adjustable delay to eliminate the initial transient). On stylus lift at the end of the LP, recording pauses, and must be manually reset. This allows time for flipping an LP, cleaning the LP or stylus, etc. without concern about spuriously retriggering the recording. The recorder is "deaf" to all input when the noise gate is closed. The noise gate also may be used for digitizing audio tapes, pausing recording when the tape reaches the end. The noise gate is not designed for voice-actuated recording (VOX) because it only opens once until reset. When it closes it must be manually (can be disabled) reset when the threshold is crossed (stylus lifted from record). It is perfectly suited to vinyl recording, however.
- Track Mark Hints Pure Vinyl Recorder also automatically creates putative track markers in a separate file (saved in the same location as the audio capture file). This expedites the track editing process in Pure Vinyl. The marker decisions are made very conservatively (from the standpoint of insuring that all track positions are marked), so that the recorder generally creates too many track markers rather than too few. However, any extra markers can very quickly and easily be deleted later, in the Pure Vinyl editor.
- Lossless Compression Sound files may be recorded in lossless (Apple Lossless Encoding) format, if desired. Such files are easily read by the Pure Vinyl editor.
- Integration with Pure Vinyl Editor and AudioLeak After completing a recording, you are asked if you want to have it automatically passed to the Pure Vinyl editor, or opened for verification in AudioLeak.
- Multithreaded for high performance and low CPU overhead Extreme pains were taken to insure that Pure Vinyl Recorder uses the minimum possible CPU resources needed for the task. It was designed to permit simultaneous capture and decimation (even from 192 kHz to 44.1 kHz). |
Recording
Shown below is a screen shot of the main Pure Vinyl Recorder window, taken while a recording is in progress. Those items which might require explanation are called out on the figure.
- Audio input and output (for monitoring) devices are indicated. They are selected and configured in Apple's Audio Midi Setup application (Applications/Utilities/Audio Midi Setup). - Peak Hold, Instantaneous Peak and RMS indicators are provided. The Peak indicators as well as peak statistics (peak hold value and clipping (Overs) count are reset with the Reset button. - The Track Split Threshold is determined automatically at the beginning of the recording, from the audio level of the lead-in groove. It is indicated by a black line on the RMS indicators. The track splits are recorded in a separate file, used with Pure Vinyl (Editor). (Audio files are not split during the recording process.) - The Inverse RIAA Make-Up Gain Adjustment is used when applying the software-based RIAA equalization curve. The make-up gain control is used to achieve appropriate signal level after the equalization. The gain is applied to files recorded with software-based inverse RIAA equalization. - The Noise Gate threshold is indicated by the aqua "water level" adjusted with the slider. The signal threshold tested against the setting is the RMS level (not Peak level). - The Noise Gate Lock is used to reset the noise gate after the "quiet" threshold has been crossed (such as happens when lifting the stylus from the record). - The file format(s) selected for recording are indicated. Here, Raw audio is being captured to a 24 bit AIFF file, and Decimated (Resampled) audio to 24 bit Apple Lossless Compression format. - The Status indicator shows either Idle, Waiting for Trigger, Triggered or Recording. |
![]() Note: the I - RIAA metering subpanel and Make-up Gain control only will be active if the software based Inverse RIAA equalization option is used. Otherwise, they will be greyed out. |
- Choose a File Format for Audio Capture
Quick tip: If you are recording LPs through a standard turntable preamp (that amplifies the signal from the turntable cartridge and applies the needed equalization), and you don't quite understand what "Inverse RIAA Equalization" means,then you would:
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Pure Vinyl provides a choice of file formats for recording.
Now would be a good time to open the Files tab of Pure Vinyl Recorder's Preferences panel, and review the options, while reading the information below. Here's a summary to help you choose the proper format:
Format and file extension | Advantages | Disadvantages |
AIFF (.aif) | A universal format compatible with essentially all audio software | Total length is limited to 4 GB. Pure Vinyl Recorder will warn you about this |
Apple Core Audio File Format (.caf) |
Supports 32 bit floating point format Supports Apple Lossless Compression |
NOT directly recognized by iTunes! Requires conversion by Pure Vinyl editor or other audio editor software |
Sound Designer II (.sd2) |
A universal format compatible with almost all audio software A plain vanilla, straighforward binary format |
Some software (not including Pure Vinyl editor) may have trouble reading Sound Designer II files with more than 31 characters in the name of the file Uses old style Mac resources in the "resource fork" of the file to provide audio format information |
M4A (.m4a) | Supports Apple Lossless Compression |
This format is not provided for recording in Pure Vinyl Recorder. The use of Apple Lossless Compression when writing large files currently is extremely memory intensive, resulting in sluggish performance. This is unfortunate, because this format is directly recognized by iTunes On the other hand, this is the native output format of the Pure Vinyl editor for rendering Apple Lossless Compressed files. Rendering shorter audio files in m4a format to Apple Lossless is not a problem |
Below is a matrix of the possible output file formats, depending on your input sample rate, and whether or not you need to use the inverse RIAA equalization feature (Audio Processing tab of the Preferences Panel).
"Raw" audio just means the audio stream is recorded exactly as input to the computer.
Input Sample Rate: 44.1 kHz | ||
Inverse RIAA | Native Sample Rate File | "Resampled" File |
Off (Unchecked) | 44.1 kHz, Raw Audio | Not Available |
On (Checked) | 44.1 kHz, Raw Audio | 44.1 kHz, RIAA Equalized Audio |
Note: in the case above with Inverse RIAA On, the "Resampled" output option is just used to save the 44.1 kHz equalized audio. The audio isn't actually resampled. |
Input Sample Rate: 48 or 88.2 kHz | ||
Inverse RIAA | Native Sample Rate File | Resampled File |
Off (Unchecked) | 48 or 88.2 kHz, Raw Audio | 44.1 kHz, Raw Audio |
On (Checked) | 48 or 88.2 kHz, Raw or RIAA Equalized Audio | 44.1 kHz, RIAA Equalized Audio |
Input Sample Rate: 96, 176.4 or 192 kHz | ||
Inverse RIAA | Native Sample Rate File | Resampled File |
Off (Unchecked) | 96, 176.4 or 192 kHz, Raw Audio | 44.1 or 96 kHz, Raw Audio |
On (Checked) | 96, 176.4 or 192 kHz, Raw or RIAA Equalized Audio | 44.1 or 96 kHz, RIAA Equalized Audio |
Important: if you wish to use the Pure Vinyl Editor with the files you're recording, and the sample rate is greater than 44.1 kHz, you also should configure the Recorder to generate a 24 bit resampled file, preferably at 44.1 kHz. This is required if sampling at 176.4 or 192 kHz. The resampled file is used to generate the vinyl platter images, and facilitates setting track or album side mark points. The resampled file also is used to create individual track files (16 bit resolution), for burning to CD or transferring to your iTunes music library, if desired. Later, during high resolution playback, the 176.2 or 192 kHz file can be played directly. See the Rendering section of this tutorial for more information. If recording at a high sample rate, the native file only is used for playback, and can immediately be archived to another disk, or other media (such as DVD-R), if desired, to free space on your hard drive. "Burn" such discs using a data format that can be mounted on the desktop. The name of the volume isn't important, but we suggest naming it the same as the name of the album, ro assist in locating it later. After rendering the album sides, to play a given album archive, insert the DVD and drag the audio file to the Pure Vinyl application icon or window. If recording at 48, 96, or 192 kHz, you will be provided a choice of different decimators. The recommended decimator is "Best" unless your computer is an older machine (and you are using 192 kHz). Use Apple's Activity Monitor application (in the Utilities folder) to monitor CPU usage. If it reaches or exceeds 50%, even briefly, use Faster or Better. Resampled files are named the same as the Raw file, except a special file identifier of "(CD)" automatically is added to the file name. This assists the Pure Vinyl editor in identifying audio files created by Pure Vinyl Recorder. The files have no inherent special formatting; the (CD) or (Raw) label is how Pure Vinyl editor identifies its "own" files. There also is an entry added to the Pure Vinyl library file that uses a unique index (the file length in microseconds) to help the Pure Vinyl Editor "recognize" its own files. |
File format suggestions: - If your audio input device only supports or is set to 16 bit resolution (verify this in Apple's Audio Midi Setup application), select a 16 bit file format. Example: AIFF, 16 bit. - If you intend to use the Pure Vinyl editor to split the audio capture file and render individual tracks later, you should select a 24-bit output format (although it isn't essential). Otherwise, use 16 bit (but use care in setting input levels). - If you want to capture audio to a lossless compressed format, you must use the Apple Core Audio File Format. This format is not currently readable by iTunes, but it is used as an intermediate format for Pure Vinyl editor. It also is supported by many other newer audio editing software packages on the Macintosh platform. Lossless compressed is the preferred format if using the Pure Vinyl editor. Example: Core Audio, Apple Lossless Compression, 24 bit. - If you want to use a different audio editor than the Pure Vinyl editor, use AIFF or Sound Designer II format. You also can try Core Audio File Format, but be sure to verify compatibility first. Example: AIFF, 24 bit. - 32 bit floating point format is inappropriate in most situations. The files are significantly larger than 16 or 24 bit integer format, and if only raw, unprocessed audio is recorded, the resolution is limited by your input device anyway (16 or 24 bit). This format is intended more as an audio mastering format, and it is included in Pure Vinyl Recorder in case someone wants to use it. |
- Recording Procedure
0. Preparation: Important!!! Use the Energy Saver panel in Apple's System Preferences to set your computer to NOT sleep the hard disks, and not go to sleep or dim the display for at least 30 minutes (a maximum length of most album sides - or whatever is the duration of the audio you anticipate capturing; this might be 125 minutes if transcribing a 120 minute DAT).
Audio capture to disk is a real-time, potentially highly-CPU-intensive process that cannot be interrupted without critically affecting the quality of the capture. You might want to launch Apple's Activity Monitor application (Applications/Utilities/Activity Monitor) to keep an eye on CPU usage. If CPU usage ever spikes above 50% during audio capture, and you are simultaneously recording to a decimated file, chances are that parts of the audio in the decimated file will be corrupted (there will be short bursts of noise in the audio file at each incident). If this happens, don't panic. The decimated file can be recreated from the raw file later, in the Pure Vinyl editor. |
1. Launch Pure Vinyl Recorder (naturally). If the audio input and monitor devices, and input sample rate aren't what you would like, Quit and configure them in Apple's Audio Midi Setup application (Applications/Utilities/Audio Midi Setup).
Important: some Macintosh computers (most notably the newer, Intel based machines) may allow setting different sample rates for the built-in microphone and Line In inputs. This should be avoided. It's important to confirm that these are set to the same sample rate (in Apple's Audio Midi Setup application); otherwise, loud pops may be emitted from the speakers. |
2. Get ready to record from your input source. For example, now is the time to clean your LP and have everything ready to go. You might also want to keep the LP jacket handy, near the computer, to use in one of the steps below.
Check your input levels and select the output file format (Preferences):
You may notice that there is no "input level" control. Pure Vinyl was based on the design premise that all signal gain adjustment should be done in the analog preamplifier stage, before being converted to digital in the audio input device. If there is insufficient signal level, it's pointless to artificially boost the digital level - because you can't retrieve what wasn't captured in the first place. So, the place to adjust the input ("Dry") signal level is at your preamplifier. Audio professionals understand this. There may be some folks that disagree with this philosophy. Accordingly, a gain adjustment is provided in Audio Processing tab of the Pure Vinyl Preferences panel. Click Apply Overall Make-Up Gain - (note that this is quite distinct from the equalization make-up gain in the main window) - and enter a value in decibels. Again, the use of this option is highly discouraged, because once the signal has passed through the A/D converter, any uncaptured audio below the device resolution limit cannot be recovered. |
3. Noise Gate. If you plan on using the Noise Gate (it can be disabled in Preferences), you need to set the gate threshold. Important: the threshold is based on the RMS signal levels (signal level bars in the window), to avoid spurious triggering that might be caused if using Peak levels. Please keep this in mind when setting the threshold.
You'll want to set the gate level with the stylus lifted from the record, because you'll want it to trigger when you lower the stylus (which triggers the recording) and again at the end of the album side, when the stylus is lifted (thereby pausing the recording). A "side" count is automatically kept, so, for example, if recording a double album, the Pure Vinyl editor will know that there were four sides (because the stylus was dropped and raised two times each).
Shown below is an example of setting the noise gate level:
Noise Gate set too low The level is below the idle RMS noise level (twin bars). This will cause the recording to immediately commence after clicking Record and naming the output file. Note that the idle noise level in your recording setup may be higher or lower than shown here. The idea is to set the noise gate level relative to the noise level of your setup. |
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Noise Gate set correctly The level is a few dB above the idle, stable, background RMS noise level (twin bars) of the audio device chain (includes turntable preamplifier). Note that here, as in the other examples, the tonearm is lifted, with no "live" audio being supplied. If your tonearm transmits noise to the stylus when handled (it shouldn't), you might have to nudge the noise gate level a bit higher than shown here. |
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Noise Gate set too high The level is significantly above the idle RMS level. This may or may not create improper triggering, depending on the noise level of the audio you plan to record. If set significantly above the background level, the noise gate may close prematurely, improperly interrupting the recording. |
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4. Click the Record button.
5. Enter the album information in the sheet window that appears. The default information always reverts to what's shown below when starting a new recording session (meaning application launch, not new recording).
Now, type in the album information:
The file in "Album:" will be created in a new (if not already existing) folder inside an eponymous folder, itself inside a folder called "Artist :" at the selected location. The default location is Users/your username/Music/Pure Vinyl/Pure Vinyl Music.
The above example would save the audio recording to Volumes/Vinyl192k/Creedence Clearwater Revival/Cosmo's Factory/Cosmo's Factory.ext where ext is the extension of the chosen file format. A file called Cosmo's Factory.plist also will be created in that folder, that contains information about the recording, including putative track markers. |
"Label:" is a very important field for record-collector geeks. Having the LP jacket handy is a good idea, unless you already have that information memorized. You can use it for any brief descriptive information, as well. If you don't care about this field, just leave it blank (but there must be something entered in the Artist: and Album: fields, to enable the Record button).
Note: these three fields can hold up to 255 characters each.
6. Click Record. The album information window closes.
Now, NOTHING will happen until you drop the stylus in the lead-in groove, because the recorder will patiently wait until the signal rises above the noise gate threshold.
7. Start the audio source. At the moment of truth, "drop" the stylus in the lead-in groove (or start playing your audio source). There is a default countdown of 2 seconds (adjustable in Preferences, and can be disabled) before the audio capture actually starts. This is designed to keep from recording the transient occurring when dropping the stylus. When the two seconds has elapsed, the computer will "beep" (can be disabled) using the selected (in Audio Midi Setup) system sound device, to confirm that the audio now is being captured to a file.
Note: the "Sloppy Cueing" Preferences option (enabled by default) allows you to recover if a stylus drop is bobbled. If you quickly lift the stylus before the two seconds has elapsed (and the beep wasn't emitted), it will be as if the stylus wasn't dropped in the first place. The "Conserve CPU" check box limits the meter update rate during recording, because meter updates can consume a significant amount of CPU on older computers. Note that every sample still is examined for signal level; the meter update rate is just slowed down a bit. If you want to conserve the maximum amount of CPU during recording (recommended), click the window's green colored "Zoom" (not the amber colored collapse) box. The recording window will resize itself, hiding the meters, only presenting the vital controls (noise gate, monitor level, Record button and signal peak statistics). |
8. Stop the audio source. At the end of the album, lift the stylus. The noise gate will immediately close and the computer will "beep," signalling a noise gate threshold transition. The result is depicted below.
The number of putative album "tracks" detected is also indicated (with the Status indicator text; not shown in the figure above). As mentioned elsewhere, the track detection algorithm is very conservative about not "missing" possible tracks, and so might indicate triple or more the number of actual tracks on the disc. This information is saved in a separate file (Album Name.plist, as mentioned above) and used by the Pure Vinyl Editor. You can ignore this information, if you like. You also can disable the auto track marking (uncheck the Auto Track Marker Threshold check box in the Audio Processing tab of the Pure Vinyl Recorder Preferences panel), and set marks manually, during recording, by tapping the space bar (whether or not auto track marking is active). |
9. Continue with the recording. Now, you can flip the record, clean the stylus, clean the record, grab a snack, etc. When you are ready to record the subsequent album side(s), just have everything ready, click LOCK (which opens the noise gate) and drop the stylus. (Lather, rinse, and repeat for each additional album side.)
Note: although there is no limit to the size of the audio file (for caf and sdII formats), for multi-disc sets captured at high sample rates, if you intend to archive to DVD format the limit for 192 kHz, 24 bit will be four typical album sides. Double-sided DVD will permit archiving longer files. You typically would want to at least archive the high sample rate audio, and include the decimated audio file if there's sufficient room on the archive media. However, you will want to do initial editing of the captured decimated file from hard disk - random seek of a file on DVD will be too slow to be practical. |
10. Stop the recording. When you are finished recording an album, click Stop. You will be asked if you want to automatically open the file in the Pure Vinyl editor or examine it in AudioLeak (if AudioLeak is located in your Applications folder). (Note: this dialog only will appear if the length of your recording is greater than approximately 10 seconds).
Clicking Verify in AudioLeak will open the file in AudioLeak without dismissing the "Send" dialog. Clicking Pure Vinyl Editor will dismiss the window, however, and if you want to examine the file in AudioLeak, you will have to manually drag the icon to the AudioLeak application icon or window later.
If you have created both Raw and decimated files, the Raw checkbox will allow examination of the Raw file, in turn.
It's highly recommended that the file be checked with AudioLeak; this only takes a few seconds. You likely will want to click the Graph Disclosure control in AudioLeak to reveal the peak levels graph (the graph drawer window can be expanded, also). You will want to check for peak levels reaching 0 dB. If this occurred in the decimated file, it likely means that something interrupted the recording process at a critical moment. See Step #0 - Preparation, above, for more information. Please read the AudioLeak Read Me file (Pure Vinyl Goodies folder) for more information on how to inspect the audio waveform and determine peak levels. |
This concludes the recording part of the workflow tutorial.